After upgrade from 10.5.1 (10.5.1.6) to 10.5.1 HF1 (10.5.1.8) using the Enterprise Manager installer, the EM_HOME/ws-plugins directory contains no files which may prevent user login via the workstation.
The upgrade caused the EM_HOME/ws-plugins directory to become empty. Engineering are investigating the root cause.
Upgrades always create a hidden backup of modified files in directory EM_HOME/backup/iscW.X.Y.Z
The ws-plugins files from the 10.5.1.6 release are compatible with the 10.5.1.8 release.
Restore the 19 *10.5.1* jar files from the backup directory EM_HOME/backup/isc10.5.1.6/ws-plugins to the EM_HOME/ws-plugins directory and then restart the Enterprise Manager/MOM.
The new Upgrade Patch for 10.5.1.6 to 10.5.1.8 that is downloadable from Support Online for APM Release 10.5, Gen level 1HF1 does not update the ws-plugins directory and does not cause this problem i.e. "APM r10.5.1.0 HF1 Upgrade Patch (for upgrade from APM build 10.5.1.6 only!)"
Upgrades from earlier versions than 10.5.1.6 to 10.5.1.8 do not encounter this problem.