problems with visual editor

I recently upgraded two blogs to wp2.6.1. One of the sites works fine but the other has a problem. Whenever I click the “write” tab in the wp dashboard I get an error that says

“a script on this page may be busy or it may have stopped responding.”

I’m then given the option to stop or continue the script. If I stop the script the image uploader doesn’t work. If I continue script it does work.
The same error happens if I save or publish a post.

any help with which script is causing the problem and how to fix it will be greatly appreciated.