I believe this is an issue with the service pack that is installed for office.
Make sure you have all your updates.

I would be interested in this answer  also as we are experiencing the
same thing sporadically.

I did find the answer. I did have info on this from the last time  it
happens. Here is what just worked to fix this problem for me:
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Fix found by: corband

I was experiencing something very similar to the issues you describe
above and the following appears to have resolved my problems:

· Go to "C:\Program Files\Microsoft Office\Office12"

· Delete "OWSSUPP.DLL"

· "Start" -> "All Programs" -> "Microsoft Office" -
> "Microsoft Office Tools" -> "Microsoft Office Diagnostics"

· Run the diagnostics and it should fix 1 issue in its last
step.

I'm running Office 2007 on XP SP2 using IE7 to access SharePoint.
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I was running office 2003 and it fixed that, so it fixes not only
Office 2007 but Office 2003.
Be sure to run the Office Diagnostics. By the way, instead of
deleting OWSSUPP.DLL, just rename it as .old or something like that,
so you can get back to were you were just in case things don't work
right after.