After upgrading to the version 6.5.700 of ZA it was no longer possible for me to build my solution. It came up with an errormsg or didn't recognize the changes I made to the code. Only rebuilding my solution was possible to see my changes. After downgrading to 6.1.744.001 everything was fine again.

Operating System:Windows XP Home Edition
Product Name:ZoneAlarm (Free)
Software Version:6.5