[PROBLEM] Shell will not start up

When i activate “Block all the unknown requests if the application is closed” in D+ i can’t get the windows shell to come up.
I can log on and the wallpaper will appear, but then nothing. It couldn’t load nvcpl.dll. Avast is updating because process explorer is showing me that. Through process explorer i can restart, jump to safe mode, start comodo and deactivate "Block ". After that i can reboot and voila.

I have a thunderbird 1 Ghz, 512 Mb ram, WinXP fully patched, Avast Pro, CFP.