ReMask is a little different than many plug-ins... I guess the lack of a user interface is part of it =) it may be a bit different than what you're used to at first.
I've written an explanation on the Topaz blog that should answer some of the more common questions about the Actions workflow and certain error messages (like the "Make" command one). Just go to the website and click "blog" if you want to read it.
The cliff notes version:
The actions are there to be used on their own. If you use actions, ONLY use actions - don't, for example, try to create a layer mask before the action. But it is possible to run ReMask without actions. If you do this, just make sure you follow this condition:
You must have a layer selected with a layer mask containing white, gray, and black. The layer itself must be selected (not the layer mask).
If you run ReMask from the Filters menu keeping the above in mind, everything will be all gravy. Hope that helped a bit!
--
Eric Yang
(Please see my Plan page for a full disclosure.)