There was an unusual behavior when i proceeded with repository manager to truncate the existing session logs. Option "Truncate Log" under "Edit" menu was disabled. Selecting/expanding the required folder also did not help.
Since my informatica server was on AIX with client on windows, i did the following to truncate the logs:
pmrep>connect -r Powercenter -d Domain_server1 -n Administrator -x Administrator
pmrep>truncatelog -t all
truncatelog completed successfully.