if it is a shell error, it's either if it is a fresh install, it was installed uncorrectly or, if it is already installed and has already programs in it, check whether you have installed a new program that is conflicting with your os, if there is uninstall it. also try to check if there has been some alterations with your system files due to viruses ro even adwares.
This sounds like a couple of worms that are out there. Have you applied all the latest microsoft security patches? If not, try disconnecting any internet connection and boot into safe mode. Install some antivirus software and then apply the latest patches.
Can you give us any more info on the error you are receiving?
windows xp has a built in reporting tool that pops up everytime it recognizes a glitch in your os with regards to a conflicting hardware or software embeded in your system. annoying it may seem i find this tool very useful since it can tell you on a technical aspect what would have possibly gone wring with your system.
but since this problem involves a shell error, i believe that this might have been caused by a virus...or hijack files that might have installed some programs within your system that is messing up windows...
try to install, as drizzle said, the latest patches for your win xp box and make sure that your AV softwares are updated...and you could also try to install adware programs to check if you have any hijack files installed in your system...
Personally I dont like the error reporting tool much.. it doesnt give you the sort of information you need to troubleshoot.. it sends off arbitrary data to an arbitrary place, and debugging a windows core dump is like trying to install DOS 5.0 on an Xbox