compatability issue?

Used your help to disinfect my computer. Worked great! Went to protect it based on the malware protection sticky and downloaded a few programs. 1st off, I'm sure I don't have another antivirus program. I used Your Uninstaller to get rid of Panda Platinum. Cleaned all traces after that. Only thing left is nagging Panda Icon in start menu tray, but computer tells me I don't have it anymore. 1st antivirus I tried just made the computer run bad. Dumped it and tried Avira which worked great for about 2-3 weeks and then couldn't connect to the internet to update. Dumped it and loaded PC tools antivirus with no issue. (Already have PC tools Firewall Plus which I love). Ran 1st scan and in the morning exited the complete and uneventful scan. Under that window was a scan result from Spyware Terminator showing an affiliate cookie which I deleted (probably a mistake). Under that window was a PC tools Firewall Plus window claiming new updates were available. Got the update and on the requisite restart locked up on 1st and 2nd tries but started 3rd time and every time since. Now everything works fine except ebay. I keep getting the message from Microsoft Visual C++ Runtime Library. It says Buffer overrun detected! Program: C:\Program Files\Yahoo!\browser\ybrowser.exe
Could this be a compatability issue or corrupt installation of PC tools antivirus or is more likely the affiliate cookie I deleted was a crucial component to browse on ebay? If so, how do you fix something like this?
Recently added programs: CCleaner, A squared free, Spyware Terminator, PC tools Firewall Plus, Your Uninstaller and PC Tools antivirus. Older protection programs: Ad Aware SE Personal, Spybot Search and Destroy, SpywareBlaster, SpywareGuard and AT&T Online Protection (everything except the antivirus). Any suggestions are greatly appreciated! Thanks.

 

Been messing around with things and I think I found the issue. Real time protection was activated for both Spyware Terminator AND PC tools antivirus. When I disabled the PC tools On Guard (real time protection), ebay began to work. But after a while On Guard turned itself back on and ebay quit working. I disabled it again, this time unchecking more boxes than before and I think it might be off for good. Question, in your opinion which of the two programs would be the best choice to leave real time protection in the ON position? Also, any ideas why PC tools antivirus turned the On Guard back on after I disabled it? (The default on the download was with On Guard turned off, I was the one who enabled it in the first place).