Unimplemeted Error with Repository Reports

Friends,
REP-09909: Unimplemeted Error with Repository Reports

I always face the Error REP-0999:Unimplemented Error when I try to 'generate a file' out of the Report Previewer. I'm using the standard Repository Reports.

The Runtime Report Version is 6.0.0.0.
Oracle Designer Version is 6 6.5.28.0
Repository Reports is 6.5.28.0, too.

Does anybody now a solution to this problem.

Thanks

Abhishek Saxena