This reply is rather late I'm sorry to say, but FTR and FWIW, Windose really, really likes double-quotes around its command line arguments (tested on Win7):

c:\@Work\Perl\monks>echo Bleach='^(GUI_|AA_|myMainScript)'
'AA_' is not recognized as an internal or external command,
operable program or batch file.

c:\@Work\Perl\monks>echo "Bleach='^(GUI_|AA_|myMainScript)'"
"Bleach='^(GUI_|AA_|myMainScript)'"

c:\@Work\Perl\monks>perl -le "print qq{>>$ARGV[0]<<};"  Bleach='^(GUI_
+|AA_|myMainScript)'
'AA_' is not recognized as an internal or external command,
operable program or batch file.

c:\@Work\Perl\monks>perl -le "print qq{>>$ARGV[0]<<};"  "Bleach='^(GUI
+_|AA_|myMainScript)'"
>>Bleach='^(GUI_|AA_|myMainScript)'<<
[download]

(Can't test with  pp ATM.)