Hi Lenore,
The problem is either the report no longer exists in that folder or permissions. The other possibility is the report is corrupted.
First of all, what version of Crystal are you using?
What version of Crystal was the original report created in?
Are you able to save a copy of the report to your local machine and open it from there?
Are you able to create a report, save it and reopen it? Can you open any other report?
Thanks,
Brian