_Base64Encode String Length

[Bitpicker]

Using iim iMacros scripts of usually 30 to 40 statements of varying lengths. These are encoded via _Bas64encode  UDF. Various iMacros errors would occur at execution leading me to isolate the iMacros errors to executing so far into the lengths of the commands. Have included a dummy string and kept lengthening until I generated error in first statement that iMacros interpreted.  

Is there a length constraint I am blowing? Autoit has stated statement length of 4095. The error occurs at around 1405 characters. I have had other code where I shortened the string the string of commands by taking out comments etc and all statements in the string ran. So believe I am up against a length constraint. Any observations will be appreciated. Test code as follows:

; ============================================================================================================
Local $sImBedMacro= _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' & @CRLF & _
'''1234567890123456789012345678901234567890123456789012345678901' & @CRLF & _
'URL GOTO=https://www.ibmsecu.org/' & @CRLF & _
@CRLF
; ====
If Not WinExists("Mozilla Firefox") Then ShellExecute ("C:\Program Files (x86)\Mozilla Firefox\Firefox.exe")
WinWait ("Mozilla Firefox")
$iMacroSCRIPT = 'imacros://run/?code=' & _Base64Encode($sImBedMacro)  ;  CONVERT the string to SCRIPT CODE
    ; ================================
    ShellExecute($iMacroSCRIPT)  ;  Run the SCRIPT CODED MACRO
    ; ================================
Sleep(3000)
Exit
;==================================================================================================================
;Calculated Length thru "'UR" of Line 17 ABOVE ~ 1405 CHARACTERS
;Produces iMacros Error: unknown command: UR, line 16 (Error code: -910)
;Windows 10 PRO 10.0.10586
;Firefox 52.0 (32-bit)
;iMacros 9.0.0.2379
;SCITE3.7.3
;Thanks

Thanks again, BitPicker

[Bitpicker]

New at Using a Forum so Please let me know if out of bounds.

Apologize for not including #include <base64.au3>  in original code and perhaps not creating Post correctly as I only see a star while all others have bold dot entry. 

After additional testing _Base64Encode IS NOT the problem. I have added test code to encode and then decode the encode result and it is exact at any length I tested.

I do have a string length problem, but I believe it is either with iMacros excuting the encoded string, or Firefox URL length accepting the imacros://run/?code= + the encoded string. 

I am using ShellExecute to fire >> imacros://run/?code=  + the base64encoded iMacro with Total Length of 3000 characters. If I include the unencoded iMacro by one character, it increases the base64encode Length by 4 and the IMacro will not complete in FireFox. It does make FireFox Window active, but no iMacro service is invoked.

So, I ask how to proceed? Should this be closed, and how to do that.

Thanks BitPicker