I've seen this a couple of times recently-it's due to a MS update and this
KB article will fix it.
Read he "resolution" paragraph carefully as it's a little tricky.

http://support.microsoft.com/?kbid=250841
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When I startup everything appears normal unless I am inactive for an
extended period of time and then Windows Explorer crashes and I get this
error message:

EXPLORER caused an exception 6d007fH in module WEBCHECK.DLL at
015f:78b32599.

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