I can't get it to fail on my computer. Maybe some security issue with the FSO? Stupied question...But you have verified the PS part is working, and the text is in the text file?

Have you tried using native kix functions only?
 Code:
$fileToCheck = "c:\temp\PSSec.txt"
$stringToFind = "RemoteSigned"

If Exist($fileToCheck)
   $stringFound = 0
   $fh = FreeFileHandle()
   $nul = Open($fh, $fileToCheck)
   While @error = 0
      $line = ReadLine($fh)
      If InStr($line, $stringToFind)
         $stringFound = 1
      EndIf
   Loop
   If $stringFound
      $nul = MessageBox("Status OK ! ", "ICT - INFO", 64, 3)
   Else 
      $nul = MessageBox("Status NOT OK ! ", "ICT - INFO", 64, 3)
   EndIf
EndIf