Are you running the utility on the Management Server?
Please make sure that you have a Client setting on the Server. Start -> Programs -> HP OpennView -> Edit Client Settings. Select "Accounts" tab, add or modify the system client settings. Type in OVSD system account name and the login password. It should work with a proper Client settings.
We were having a huge problem with this (OVSD 5.1 sp1). For about 100 distinct users logged in the system, "Logged On Users" was showing 500 and higher. We only recently got a hotfix that helped us out, but we still see illegitimate duplicates from time to time.