Web page gets blanked out without saving when pressing save button.

I have a web form with a dropdown list, two textboxes, checkbox list, and gridview and a save button at the bottom. 
Sometimes when a user types in information and clicks save button, all the information gets wiped out and not saved.  Where do I even begin to debug this?  I am using ASP.net 2.0.   
Please help! 
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