One thing I came across once was that the report didn't appear to open, but I noticed scroll bars on the main Db window. When I scrolled down and accross,(a long way), the reports were there. (Dont ask me how they got there).
One other thing to check is any code on the "On Open" event or "On Activate" event of your report. If there is an error, and it is not properly trapped, the report will fall over.
HTH
Dave