ERROR:Xst:827 = Signal count cannot be synthesized

I am trying to simulate an elevator and as a result i get the error

ERROR:Xst:827 = Signal count cannot be synthesized, bad synchronous description

I am following the code from this source [https://www.youtube.com/watch?v=i03_-NMwmDs] since mine is very similar,(i have 7 floors and two more elevators). At first i am working with the code mentioned on the video and later i am going to implement two more elevators to work together in this simulation.

Thanks in advance.

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity elevator is
port (clk: in  std_logic;
sensors1: out std_logic:='0'; --sensors at each level for elevator 1
a1, a2, a3, a4, a5, a6, a7: out std_logic; -- for LED display at FPGA
insideopendoor, in1, in2, in3, in4, in5, in1up, in2up, in3up, in4up,        in5up, in5down, in4down, in3down, in2down, in1down: std_logic;  -- input request for each floor
opendoor: out std_logic; -- from inside elevator
closedoor: out std_logic);  -- from inside elevator
end elevator;

architecture sequence of elevator is

constant timedoorclose: integer := 3;  
constant timedoorclosed: integer := 2;   
constant time_nx_state: integer :=4;
signal demand: std_logic_vector(0 to 4) := "00000";
signal direction_of_elevator :  integer range 0 to 2 := 0;
signal updownpassenger : std_logic := '0';
signal signalstatus: std_logic := '1';
type status is (L1, L2, L3, L4, L5);
signal pr_state, nx_state: status;

begin

main: process (clk, insideopendoor, in1, in2, in3, in4, in5, in1up, in2up, in3up, in4up, in5up, in5down, in4down, in3down, in2down, in1down)
variable digit1 : std_logic_vector (6 downto 0);
variable count : integer range 0 to (time_nx_state + timedoorclose + timedoorclosed);
variable bufferopendoor : std_logic;
variable position : integer range 0 to 4;
variable tempup : integer range 1 to 2 := 1;
variable tempdown : integer range -4 to 4;

begin

if (clk'event and clk='1') then
    demand(0) <= demand(0) or in1 or in1up or in1down;
    demand(1) <= demand(1) or in2 or in2up or in2down;
    demand(2) <= demand(2) or in3 or in3up or in3down;
    demand(3) <= demand(3) or in4 or in4up or in4down;
    demand(4) <= demand(4) or in5 or in5up or in5down;

            case pr_state is 
                when L1 => position := 0;
                when L2 => position := 1;
                when L3 => position := 2;
                when L4 => position := 3;
                when L5 => position := 4;
            end case;

                for i in 1 to 4 loop
                    if demand(i) ='1' then
                        tempup := i - position;
                    else null;
                    end if;
                end loop;

                            for i in 3 downto 0 loop
                                bufferopendoor := '1';
                                closedoor <= '0';
                                count := 0;
                            end loop;  --


elsif (updownpassenger = '1') then
            if (count < timedoorclose) then
                opendoor <= '1';
                bufferopendoor := '1';
            elsif count < (timedoorclose + timedoorclosed) then
                opendoor <= '0';
                bufferopendoor := '0';
            else
                closedoor <= '0';
            end if;
--else null;    ------
--end if;     ------

-----------part main-----------------
count := count +1;
        if insideopendoor = '1' then
            opendoor<='1';
            bufferopendoor :='1';
            closedoor <= '0';
            count := 0;
        elsif (updownpassenger ='1') then
                if (count < timedoorclose) then
                    opendoor <= '1';
                    bufferopendoor := '1';
                    closedoor <= '0';
                elsif (count < (timedoorclose + timedoorclosed)) then
                    opendoor <= '0';
                    bufferopendoor := '0';
                    closedoor <= '1';
                else
                    closedoor <= '0';
                    pr_state <= nx_state;
                            if signalstatus = '1' then
                                signalstatus <= '0';
                            else
                                signalstatus <= '1';
                            end if;
                    count := 0;
                end if;
        else null; --
        end if;--

        case nx_state is

            when L1 =>
            digit1 := "1111001";
                    if demand(0) = '1' then
                    demand(0) <= '0';
                    else null;
                    end if;

            when L2 =>
            digit1 := "0100100";
                    if demand(1) = '1' then
                    demand(1) <= '0';
                    else null;
                    end if;

            when L3 =>
            digit1 := "0110000";
                    if demand(3) = '1' then
                    demand(3) <= '0';
                    else null;
                    end if;

            when L4 =>
            digit1 := "0011001";
                    if demand(3) = '1' then
                    demand(3) <= '0';
                    else null;
                    end if;

            when L5 =>
            digit1 := "0010010";
                    if demand(4) = '1' then
                    demand(4) <= '0';
                    else null;
                    end if;
            when others => null;
        end case;

a1 <= digit1(0);
a2 <= digit1(1);
a3 <= digit1(2);
a4 <= digit1(3);
a5 <= digit1(4);
a6 <= digit1(5);
a7 <= digit1(6);
end if;
end process main;

step: process (pr_state, signalstatus)

begin

case pr_state is
--end if;

when L1 => 
if (demand(0)='1') then
    nx_state <= pr_state;
    updownpassenger <= '1';
else 
    updownpassenger <= '0';
    if direction_of_elevator = 1 then
        nx_state <=L2;
    elsif direction_of_elevator = 2 then
        nx_state <= pr_state;
    else
        nx_state <= pr_state;
    end if;
end if;

when L2 => 
if (demand(1)= '1') then
    nx_state <= pr_state;
    updownpassenger <= '1';
else 
    updownpassenger <= '0';
    if direction_of_elevator = 1 then
        nx_state <= L3;
    elsif direction_of_elevator = 2 then
        nx_state <= L1;
    else
        nx_state <= pr_state;
    end if;
end if;

when L3 => 
if (demand(2)= '1') then
    nx_state <= pr_state;
    updownpassenger <= '1';
else 
    updownpassenger <= '0';
    if direction_of_elevator = 1 then
        nx_state <= L4;
    elsif direction_of_elevator = 2 then
        updownpassenger <= '1';
    else
        updownpassenger <= '0';
        if direction_of_elevator = 1 then
        nx_state <= L5;
        elsif direction_of_elevator = 2 then
        end if;
    end if;
end if;

when L5 => 
    if (demand(4)='1') then
        nx_state <= pr_state;
        updownpassenger <= '1';
    else 
        updownpassenger <= '0';
            if direction_of_elevator = 1 then
                nx_state <= L4;
            elsif direction_of_elevator = 2 then
                nx_state <= L1;
            else
                nx_state <= pr_state;
            end if;
    end if;     
    when others => null;        
end case;
end process step;
end sequence;

Your code seems very mixed up. There is a specific reason why it won't synthesise: think carefully when the code immediately following this line here

elsif (updownpassenger = '1') then

will be executed. It will be executed following a positive edge or negative edge on any input in the sensitivity list, apart from clk where it will be executed only following a negative edge. How would you design logic with such behaviour? You synthesiser can't do it, either.

Basically, you need to refactor your code. You need to split it into sequential and combinational processes. (Combinational logic is logic whose output depends only on it's input and thus is logic that contains no latches or flip-flops. Sequential logic is logic that contains latches or flip-flops, but will also usually contain some gates too. Do not use latches - they are not synchronous design.) Whilst there are many ways to code such processes, it is wise to be consistent by sticking to a template. Here are three templates, which if followed, will give you everything you need and will keep your VHDL coding life simple:

Here is the template for sequential logic with an asynchronous reset, which all synthesis tools should understand:

process(clock, async_reset)  -- nothing else should go in the sensitivity list
begin
    -- never put anything here
    if async_reset ='1' then  -- or '0' for an active low reset
        -- set/reset the flip-flops here
        -- ie drive the signals to their initial values
    elsif rising_edge(clock) then  -- or falling_edge(clock) or clk'event and clk='1' or clk'event and clk='0'
        -- put the synchronous stuff here
        -- ie the stuff that happens on the rising or falling edge of the clock
    end if;
     -- never put anything here
end process;

Here is the template for sequential logic without an asynchronous reset:

process(clock)  -- nothing else should go in the sensitivity list
begin
    -- never put anything here
    if rising_edge(clock) then  -- or falling_edge(clock) or clk'event and clk='1' or clk'event and clk='0'
        -- put the synchronous stuff here
        -- ie the stuff that happens on the rising or falling edge of the clock
    end if;
     -- never put anything here
end process;

And here is the corresponding template for a combinational process:

process(all inputs in the sensitivity list)  -- an 'input' is a signal either on the LHS of an assignment or a signal that is tested
begin
     -- combinational logic (with complete assignment and no feedback)
end process;