If you're using paid OD Plus now, did you have the free version installed before? If so, did you uninstall the free version before installing the paid version? If not, save and backup any themes and icons you want to keep, uninstall the OD Plus (and the OD free if it's still showing out there), reboot, and try re-installing the Plus.

Also, on XP the systray function will only work if you are logged in as a user with Administrator rights.  If you are logged in as a Limited user, you can make the systray work by starting ObjectDock using the right-click "Run As" option and using an administrator user and password.  If you use the "Run As", you are actually using, modifying, and saving the Admin user's docks.  If you want, you can also create a systray dock in the Admin User, use the "Run As" once to load the Admin dock each time the Limited user logs on, exit ObjectDock, and then start it up again normally and the systray will work during the current login session and use the current user's docks- the Admin rights need to be there just once during a current Limited user logon to get the systray services started up, and those services only start up when a systray dock is loaded.