Guys, thanks for helping me out. May I give you some additonal information:
System:Windows 7 64 bit, 4 GM RAM
ProjectMaker Version 3.60.701 (error only happens when I run ProjectMaker in debug mode)
Software running in background: SenukeX and iMacros
The error happened sometimes when I enter a captcha code or click a site button that leads me to the next page of a website.
I really hope we can find the source of the error coz I just LUV ZP
Ok, I guess the source of the problem was some outdated driver. I updated all drivers on my system and I´m running ZP for the past two weeks with no problems. Thanks you Hungry Bulldozer for pointing me to the right direction.