If you already upgraded Enforce, and are trying a local upgrade copy the monitor.ver file to the upgrade directory and try the upgrade again. It should successfully complete.
As Manoj mentioned I strongly recommend to follow step by step teh upgrade guide when upgrading to 11.5 manually. Try to uncompress the jar file into /DLP_home/Protect/updates/detectionupgrade11.5/.
Files may be extracted into a folder named DLP. Copy all thosse files and folders to the detectionupgrade11.5 folder and re run the upgrade.
I hope this information helps,
Greetings,
Chopper