Hi...I met this situation some times.Especially the earlier versions of SCR.
First make sure that you don't have an idle parameters in your report.If u have, delete them.Also you must also remove formulas that are not used in your report.
Maybe another reason is the modification of db.Then "verify database" command should be acted.
If you run your report from a web browser ,maybe you are sending an incorrect query string.
Those are the first things I remember my actions when I solve this sort of problem.
Maybe they all may not solve your problem.If they don't please let me know.Greetings.