Bad groupset 8162774324608996 found in bug 12600

[ajaya at renewal-iis.com]

HI Friends,
 We had been using bugzilla for defect tracking from last one year and it has lot of production data. Two days back we started facing problem
  the problem is
 once a issue is logged and than  we  try to go back on to that, it says "

Permission denied.

Sorry; you do not have the permissions necessary to see bug 12600. "
 while the user have permission on the project and    when I run sanity check than it gives error
 Bad groupset 8162774324608996 found in bug 12600  It is giving this error for all the new bugs/review defects.
 This is urgent as production  server  is down. Please  suggest
 -Ajay