@gunju2221 we’re in trouble-shooting mode and just crossing out what could have happened to your installation. Sometimes it could be the simplest of things to an issue that requires creating a ticket in trac. All volunteers who help out in these forums asnwer based on what your posted. The more specific info we have on your install, the better. Moving on, have you tried deactivating other plugins except BuddyPress and tried creating a topic? There could be a conflict with plugin which has not been updated for BP 1.2.6.