This is an odd problem, but can be reproduced reliably (and has been by many of my users)
I cant describe it very well, so its best I supply an example file.
Clicking one of the buttons does an ajax post.
All works fine in firefox.
In internet explorer 7 and 8, and jquery 1.4.2, the buttons will fail with a jQuery exception.
The exception occurs when it tries to create an XMLHTTPObject, and the error is 'object does not support this property or method)
Usually if you force a reload of the page, by holding SHIFT+refresh, oddly, the buttons will then start working.
Then go to the browser address bar, and hit enter so its basically using a cached copy, and the buttons will fail again.
The reload issue is not actually cache related that I can tell. Disabling the browser cache completely produces the same results (?!).
Reverting to jquery 1.2.6 resolves the problem (although there might be later versions which work too)