There are some Enque and dequeu lock/unlock function modules which are RFC enabled, but not all of them.
When you create a Lock object you need to provide Allow RFC tick in the Attributes tab, only then the FM created will be RFC enabled. if you press F1 on the check box allow RFC you will get additionalk info. For eg.
If you activate Allow RFC for an exisitng lock object, you must make sure that the call of the generated function module has parameters of the right type. Before you activate the lock object with the new option, you should check all the programs that use the corresponding function modules.