unable to create invoice after upgrade

We have recently upgraded from 11i to R12.2.3. Once the upgrade is done, i have navigate to Payables Invoice screen and selected the required fields like invoice type, Supplier Site etc. But once the supplier site is selected form is not allowing to move to another field. Even though i manually click on any other field with in the invoice, system is not allowing to select any other field. Request your inputs if i am missing any relavant setups.

Thanks and Regards

Prasad