Oracle Report 6i: No data Issue after migrating from RBO to CBO (9i Database)

Dear All,

We switched our instance to Cost Based Optimizer recently. Also, I have scheduled daily gathering of database statistics. Over all, for more than 3 weeks, we did not face any issues with our ERP application "ORION" and i have noticed significant performance improvements. Since last week, few of our Oracle Reports have been showing unexpected behavior. Usually, they run fine, but suddenly they show no data. If i run the underlying query, I get the data. In the same period, our SGA reached 90% full and i flushed it as one of the user was getting ora-04031 error, and continued with testing on those reports. This time i could see the data in the reports.

What i wanted to know was, has any one noticed CBO having an impact similar to my case, or could their be any other reasons for Oracle Report's such weird behavior?

Please assist.