It looks like deleting everything related to Syncrosoft, LCC, or eLicenser does the trick. 6.0.1.8 is now working with 10.6.1 on my Mac Pro. I deleted the app, everything in Application support, anything in both user and system logs, anything in receipts, including all related entries in the InstallHistory.plist (and then saved the file), and the plist file in user prefs (Thanks, Richard). It then installed OK and is working fine.
Jon
I've tried this, following your instructions, but the problem persists on my MacBook Pro, eLicenser Control Center and my USB Key.
Please, can you describe more precisely every folder and file you've deleted, step by step? Do you restarted your Mac before reinstall eLicenser Control Center? Thanks!