Wrong index is being picked up

Hi Friends,

We are running oracle 11g 11.2.0.3.0 on Linux having CRM 5.0 and ECC 6.

There are oracle RAC having 9 nodes and 28 SAP APPs instances for CRM and 8 for SAP ECC.

We are facing performance challenge  in transaction code FBL5N in ECC and in CRM we are facing same issue for customer and partner not able to enter meter reading.

We have analyzed both issue in found that it is using wrong index. After making wrong index invisible it is using correct index and performance is also fine.

Now we are not able to find how it picked up wrong index in both cases and nothing has changed in programs and database level.

Regards

Ganesh Tiwari