When a system tells users they should look into the report parameters as the reason the report isn't displaying.  It's reasonable for your users to believe you aren't misleading them. 

The report viewer error message misleads users.  In reality the parameters are correctly configured and it the repot URL could be wrong.  Or a variety of other issues are at play; for instance, a problem with you connection string will also return the "Unable to get report parameters" error message.  I'd like to see this error message at minimum changed to "report can't display."   It's better to throw out a generic message vs having users spend hours or days troubleshooting the report parameters.  Better yet a proper catch/validation system put into place please.