“Not enough storage is available to complete this

The below code is for converting a zip file to base64 format.

Dim inByteArray, base64Encoded,
Const TypeBinary = 1
inByteArray = readBytes("F:path/file.zip")
base64Encoded = encodeBase64(inByteArray)

Private Function readBytes(file)
    Dim inStream
    ' ADODB stream object used
    Set inStream = CreateObject("ADODB.Stream")
    ' open with no arguments makes the stream an empty container 
    inStream.Open
    inStream.Type = TypeBinary
    inStream.LoadFromFile(file)
    readBytes = inStream.Read()
End Function

Private Function encodeBase64(bytes)
    Dim DM, EL
    Set DM = CreateObject("Microsoft.XMLDOM")
    ' Create temporary node with Base64 data type
    Set EL = DM.CreateElement("tmp")
    EL.DataType = "bin.base64"
    ' Set bytes, get encoded String
    EL.NodeTypedValue = bytes
    encodeBase64 = EL.Text
End Function

I tried first with a zip file of size 3MB It worked fine . But when I try with a zip file of size 34 MB it says

Not enough storage is available to complete this operation!

at line

encodeBase64 = EL.Text

Is there any way that I can handle zip files of all sizes because my file sizes are mostly 30MB or more.

edited 2017/01/10 - (original answer keeped at bottom)

edited 2017/01/10 - (again) - some (not all) of my problems with timeouts were caused by a disk failure.

Problems with input data were handled by splitting the conversion operations. Now code has been changed to handle buffering in two different ways: for small files (by default configured for files up to 10MB) a memory stream is used to store the output, but for big files (greater than 10MB) a temporary file is used (see notes after code).

Option Explicit

Dim buffer
    buffer = encodeFileBase64( "file.zip" ) 

    WScript.StdOut.WriteLine( CStr(Len(buffer)) )


Private Function encodeFileBase64( file )
    ' Declare ADODB used constants
    Const adTypeBinary = 1
    Const adTypeText = 2

    ' Declare FSO constants
    Const TEMP_FOLDER = 2

    ' Initialize output
    encodeFileBase64 = ""

    ' Instantiate FileSystemObject
    Dim fso
    Set fso = WScript.CreateObject("Scripting.FileSystemObject")

    ' Check input file exists
    If Not fso.FileExists( file ) Then 
        Exit Function
    End If 

    ' Determine how we will handle data buffering.
    ' Use a temporary file for large files 
    Dim useTemporaryFile
    useTemporaryFile = fso.GetFile( file ).Size > 10 * 1048576

    ' Instantiate the B64 conversion component
    Dim b64 
    Set b64 = WScript.CreateObject("Microsoft.XMLDOM").CreateElement("tmp")
        b64.DataType = "bin.base64"

    Dim outputBuffer, outputBufferName
    If useTemporaryFile Then 
        ' Create a temporary file to be used as a buffer
        outputBufferName = fso.BuildPath( _ 
            fso.GetSpecialFolder( TEMP_FOLDER ), _ 
            fso.GetTempName() _ 
        )
        Set outputBuffer = fso.CreateTextFile( outputBufferName, True )
    Else 
        ' Instantiate a text stream to be used as a buffer to avoid string 
        ' concatenation operations that were generating out of memory problems
        Set outputBuffer = WScript.CreateObject("ADODB.Stream")
        With outputBuffer
            ' Two bytes per character, BOM prefixed buffer
            .Type = adTypeText
            .Charset = "Unicode"
            .Open
        End With 
    End If 

    ' Instantiate a binary stream object to read input file 
    With WScript.CreateObject("ADODB.Stream")
        .Open
        .Type = adTypeBinary
        .LoadFromFile(file)

        ' Iterate over input file converting the file, converting each readed
        ' block to base64 and appending the converted text into the output buffer
        Dim inputBuffer
        Do
            inputBuffer = .Read(3145716)
            If IsNull( inputBuffer ) Then Exit Do

            b64.NodeTypedValue = inputBuffer
            If useTemporaryFile Then 
                Call outputBuffer.Write( b64.Text )
            Else 
                Call outputBuffer.WriteText( b64.Text )
            End If 
        Loop 

        ' Input file has been readed, close its associated stream
        Call .Close()
    End With

    ' It is time to retrieve the contents of the text output buffer into a 
    ' string. 

    If useTemporaryFile Then 
        ' Close output file 
        Call outputBuffer.Close()
        ' Read all the data from the buffer file
        encodeFileBase64 = fso.OpenTextFile( outputBufferName ).ReadAll()
        ' Remove temporary file
        Call fso.DeleteFile( outputBufferName )

    Else 

        ' So, as we already have a Unicode string inside the stream, we will
        ' convert it into binary and directly retrieve the data with the .Read() 
        ' method.
        With outputBuffer
            ' Type conversion is only possible while at the start of the stream
            .Position = 0
            ' Change stream type from text to binary
            .Type = adTypeBinary
            ' Skip BOM
            .Position = 2
            ' Retrieve buffered data
            encodeFileBase64 = CStr(.Read())
            ' Ensure we clear the stream contents
            .Position = 0
            Call .SetEOS()
            ' All done, close the stream
            Call .Close()
        End With 
    End If 

End Function

Will the memory be a problem?

Yes. Available memory is still a limit. Anyway I have tested the code with cscript.exe running as a 32bit process with 90MB files and in 64bit mode with 500MB files without problems.

Why two methods?

The stream method is faster (all operations are done in memory without string concatenations), but it requires more memory as it will have two copies of the same data at the end of the function: there will be one copy inside the stream and one in the string that will be returned
The temporary file method is slower as the buffered data will be written to disk, but as there is only one copy of the data, it requires less memory.

The 10MB limit used to determine if we will use or not a temporary file is just a pesimistic configuration to prevent problems in 32bit mode. I have processed 90MB files in 32bit mode without problems, but just to be safe.

Why the stream is configured as Unicode and the data is retrieved via .Read() method?

Because the stream.ReadText() is slow. Internally it makes a lot of string conversions/checks (yes, it is advised in the documentation) that make it unusable in this case.

Below it is the original answer. It is simpler and avoids the memory problem in the conversion but, for large files, it is not enough.

Split the read/encode process

Option Explicit
Const TypeBinary = 1

Dim buffer
    buffer = encodeFileBase64( "file.zip" ) 
    WScript.StdOut.WriteLine( buffer )

Private Function encodeFileBase64( file )

    Dim b64 
    Set b64 = WScript.CreateObject("Microsoft.XMLDOM").CreateElement("tmp")
        b64.DataType = "bin.base64"

    Dim outputBuffer
    Set outputBuffer = WScript.CreateObject("Scripting.Dictionary")

    With WScript.CreateObject("ADODB.Stream")
        .Open
        .Type = TypeBinary
        .LoadFromFile(file)

        Dim inputBuffer
        Do
            inputBuffer = .Read(3145716)
            If IsNull( inputBuffer ) Then Exit Do

            b64.NodeTypedValue = inputBuffer
            outputBuffer.Add outputBuffer.Count + 1, b64.Text 
        Loop 

        .Close
    End With

    encodeFileBase64 = Join(outputBuffer.Items(), vbCrLf)
End Function

Notes:

No, it is not bulletproof. You are still limited by the space needed to construct the output string. For big files, you will need to use an output file, writing partial results until all the input has been processed.
3145716 is just the nearest multiple of 54 (the number of input bytes for each base64 output line) lower than 3145728 (3MB).