Delete xml node from SQL Server 2008 r2 table colu

I have an xml structure as follows

<DifficultyRule xmlns="urn:gjensidige:processguide:201201">
 <Id>fc39f423-05c0-4de9-ae46-12fe3c0c279b</Id>
 <Code>5595e558-7d10-4767-86dc-5d16f24b8151_Code</Code>
 <Author />
 <Updated>9/5/2012</Updated>
 <Sequence>0</Sequence>
 <FromControls>
 <Control>
  <Code>oiuyui</Code>
  <Id>70579cbe-c0b5-4b49-a7b8-6201af388f59</Id>
  <FilterValues>
     <FilterValue xmlns:p5="urn:gjensidige:processguide:201201" p5:Id="b897f3ac-b40f-4b96-b438-eb156a26457e" p5:Code="e" p5:LookupId="3fa26ce7-4031-4e41-92cb-50d8ce56d262" />
   </FilterValues>
 </Control>
</FromControls>
<DifficultyCode>Red</DifficultyCode>
</DifficultyRule>

I am trying to delete the FilterValue node in the xpath

/qn:DifficultyRule/qn:FromControls/qn:Control/qn:FilterValues/qn:FilterValue

based on the value of the p5:Id attribute but I am confused as to why nodes are not getting deleted.

Below is the script I'm using:

declare @lookupvalueId varchar(50)
declare @ruleId varchar(50)

set @lookupvalueId = 'b897f3ac-b40f-4b96-b438-eb156a26457e'
set @ruleId = 'fc39f423-05c0-4de9-ae46-12fe3c0c279b'

;WITH XMLNAMESPACES ('urn:gjensidige:processguide:201201' as qn)
update pdr_processdefinitionrule
set PDR_RuleXml.modify('delete (/qn:DifficultyRule/qn:FromControls/qn:Control/qn:FilterValues/qn:FilterValue[@Id=sql:variable("@lookupvalueId")])')
where pdr_guid = @ruleId

What am I missing? Any guidance will be appreciated

Well, since your XML attribute id is the XML namespace with the prefix p5, you must also declare and use that second XML namespace in your code:

declare @lookupvalueId varchar(50)
declare @ruleId varchar(50)

set @lookupvalueId = 'b897f3ac-b40f-4b96-b438-eb156a26457e'
set @ruleId = 'fc39f423-05c0-4de9-ae46-12fe3c0c279b'

;WITH XMLNAMESPACES ('urn:gjensidige:processguide:201201' as qn,
                     'urn:gjensidige:processguide:201201' as p5)
update 
    pdr_processdefinitionrule
set 
    PDR_RuleXml.modify('delete (/qn:DifficultyRule/qn:FromControls/qn:Control/qn:FilterValues/qn:FilterValue[@p5:Id=sql:variable("@lookupvalueId")])')
where 
    pdr_guid = @ruleId

See that second XML namespace definition for p5? See the use of that XML namespace in the qn:FilterValue[@p5:Id=sql:variable("@lookupvalueId")] expression?