Windows Vista The application failed to initialize properly (0x00005)

When ever I try to open certain programs it comes up with this message: the application failed to initialize properly (0x0005) Click OK to terminate.<--(I don't know how many zeros) It started ever since I downloaded Bit Defender (virus stuff). At first I couldn't open things like the Control Panel through the start menu but I could through the browser window. I also couldn't click on anything in the Control Panel that had the security shield beside it. Then I ran a scan and it found 6 trojan viruses and got rid of them, I uninstalled AVG (I had that before) and my computer was fine. Then the next day it started doing it again when logged on, tried to open Windows Live Mail, and my Firefox Add ons aren't working. I'm sure there's still more wrong but I haven't had the time to figure it out yet. Any ideas on what I can do?