Yes it may be possible, installing and updating antivirus may have figured our corruption in urlmon.dll deleted the file or did some changes due to which you are getting the critical error
You can try 2 things,
1. Restore earlier settings, which may uninstall your antivirus and you need to install again. But if this works recommend you to first scan the system with free standalone antivirus availalable and then install your version of antivirus. Try following link
2. Repair the URLMON.DLL file
1.Insert your Windows XP CD in your CD-ROM drive and boot your computer from the CD.
2.When the Welcome to Setup screen appears, press R to open the Recovery Console.
3.When prompted for an administrator password, type the password and then press Enter. In case no administrator password was set, just press Enter.
4.At the Command Prompt, type the following command and press Enter
5.Next, type the following command to rename the urlmon.dll file and press Enter.
ren urlmon.dll urlmon.old.dll
6.Now, to restore the original urlmon.dll, type the following command and press Enter.
expand [CD drive letter]:\i386\urlmon.dll %systemroot%\system32 /Y
7.Next, type exit and press Enter.
8.Restart your computer.
3. Repair complete OS. You will need XP CD
Boot from CD and follow the instructions to repair the OS