Runtime Error Preventing IE From Opening

Starting this afternoon, I cannot open Internet Explorer.
When I click on the shortcut icon, as well as the exe file, I get the following pop-up:
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Microsoft Visual C++ Runtime Library
Runtime Error!
Program: C:\Program Files\Internet Explorer\iexplorer.exe

This application has requested the Runtime to terminate it in an unusual way. Please contact the application’s support team for more information.
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Outlook Express works fine (have received and sent emails), and I have web access thru Firefox (downloaded onto and emailed from another computer after this problem started).

I keep Norton Anti-virus updated, and ran Ad-Aware and Spybot with nothing being detected.

I'm running XP/SP2, and updating with any security updates from MS on a regular basis. I haven't done anything different to my computer over the past 24 hours that I can recall.

Any ideas?

Many thanks.