Question radio buttons not working

We have a course that is having a problem with MC questions. The radio buttons and the Submit button seem to go inactive sometimes. Mouse over them, click on them, nothing happens.I have checked carefully for overlapping text boxes or other objects. None that I could find.It works fine on our machines (although sometime back we too had the problem but it just went away). It works on our machines in IE6, IE7, and Firefox off and on the server. When we provide the link to testers, they have the above problems with most all the questions.Anyone experienced this, know what might cause this and is there a workaround?

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