Explorer.exe error on shutdown

You may have a problem with one of your memory chips. See the link below for a free tool and guide on how you can test your RAM.
http://oca.microsoft.com/en/windiag.asp

Some other things I'd do just to help remedy any issues would be to make sure that your Windows is completely up to date.

scnrfrq--This message or something similar appears in many situations.  So it is hard to pick one fix.
Here are a few individual ideas if the above suggestions do not help
https://www.experts-exchange.com/questions/21054987/Getting-explorer-exe-Application-Error-under-Windows-XP-Pro.html
http://www.winportal.com/chat_sin.asp?ObjectID=4318
A very long list of other possibilities is http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2006-38,GGLG:en&q=Explorer%2eEXE+%2d+Application+Error+the+memory+could+not+be+read%2e

Having said that, you might try repairing your WinXP installation.  Start|Run|type SFC /SCANNOW   |OK.
You may be asked for your WinXP CD.

I've run sfc and a repair from the Recovery Console. Still getting the error, along with a Runtime 216 error.

scnrfrq--The RunTime error message could be an indication of a trojan virus.
An ancient reference is http://support.microsoft.com/kb/259279
But it still could be a possibility.  
Scan your PC with antivirus and antispyware apps with up to date reference definitions.  Delete what they suggest.  If any malware IS detected, it probably would be best to then run HiJackThis.  http://www.download.com/Trend-Micro-HijackThis/3000-8022_4-10227353.html
You can post the log here and someone will assist with an analysis.

I've done multiple scans - no viruses or spyware are found

I have just finished testing, and have concluded that this error was being caused by IZArc. This zip utility added a shell extension and right click menu entry, and was found by others to cause this error also. This occurred even though Izarc was not even running. I deleted IzArc and no more errors..