>>Which part is the error taking place in - the Shell call or the targeted program? If the targeted program does it return an error level (you could test this with ERRORLEVEL in a batch file) ?
>
>I'm not sure how can I use ErrorLevel for something useful and do I have to create a bat file on the fly in order to ger ErrorLevel?

Create a batch file that calls the zip you want to do.
Force the zip to fail (give it a bad file, takeout floppy, etc.)
Type out the ERRORLEVEL and see if you get different results depending on the error or if it gives same result no matter what happens, even if successful.

maybe something like:
zipit filesource a:\target
@echo %ERRORLEVEL%