If …
(a) you are running Avast! antivirus and
(b) you have XP SP2 and
© your experience is the same as mine
you will find that one of these Windows updates
Windows XP family Windows Malicious Software Removal Tool (KB890830)
Windows XP family Security Update for Windows XP (KB901214)
Windows XP family Security Update for JView Profiler (KB903235)
Windows XP family Update for Windows XP (KB898461)
will blow your Avast! installation to smithereens, so you may want to make a note of your settings for when you reinstall it.
[rant mode]
A short message to M$… I will continue to use Avast! despite your best efforts because it is free and it works. And I only have IE still on my machine because when I check your update site you don’t support Firefox, which is also free and also works. [/rant mode]
Hi PeeGee, thanks for the info and avast recomendation (great bit of software) 
But … I have XP SP2 and all bang up to date, and Avast works fine with it … two things that may be different …
I did a new install on Friday, and put avast on after windows was all updated, which might be some of it, and also I disable the windows security centre monitoring of updates/anti-virus/firewall etc, which may contribute ?
Polite Reminder: if SP2 breaks something check first that DEP is not closing down the program… find the executable and add it to the DEP Allowed list if you’re brave/foolhardy - like when it breaks the MSFF2 stick Profiler for example
Ming
avast is a superb bit of kit
far better than that norton guff
DEP Ming?
I’ve been having odd troubles with windows recently when someone sends a file over msn… sometimes it tells me “windows has (seemingly randomly) condemned this file to the depths of hell for no particular reason, if you think the file is safe, navigate to where it should be only to find it actually isn’t there to maximise your annoyance” or similar…
any way to shut that off (sorry for thread hijack )
DEP Ming?
Data Execution Prevention mate. Security feature.
http://support.microsoft.com/kb/875352
Ming