Have you entered any data/value in any of the fields manually (or) populated by default .
To clear the fields, You may use clear record and retry to resolve this.
Check you have no triggers, either at item, block or form level, that might be "brushing" the record before querying.
Thanks for the info , actually i'm populating the User name field based on the FND USER LOGIN, when i cleared the records i was able to enter into query mode.
Thanks for sharing the details.