Hi Sreenivasa,
It could be anything from a connectivity issue from the server you have HANA studio installed to the HANA System or an actual issue on the HANA system
How about the HANA backup console? do you see the backups taking place regularly especially the log backups...
After you have verified the connectivity to HANA system from another source server and if you find similar issues try to get the Indexserver trace file and check if you have any errors howing up in the trace file
This would be a good point to start troubleshooting
Sunil