I think my problem has been solved by loading the extra (missing) jars and restarting OTM.
The jars are listed in
(OTM v5.5 Extra Jars Required for Installation)http://www.otmfaq.com/forums/f23/otm-v5-5-extra-jars-required-installation-415/
(Please note make sure you get the latest versions of these jar files)
For the record, it works fine now in both passive and active modes.