Wasim,
The error that we are getting is generally due to huge accumulation of logs in ACS
installation folder :
Please remove or relocate all the logs file from following location and then try to upgrade, :
\CSAuth\Logs
\CSRadius\Logs
\CSTacacs\Logs
\CSLog\Logs
\CSMon\Logs
\CSAdmin\Logs
\CSDbsync\Logs
Regards,
~JG