Hi Srikanth,
The 30270 is one of the most generic error messages you will find - and searching may not bring much help to you.
Something has changed on your Webi report, do you have a version in your Development client that you can check.
If you can't open it in Modify mode then you are in bother, if the report isn't too big - I would just take the hit and rebuild it. I have searched many a time for help with this error message and have yet to find one sure fire fix.
With regards,
Gill