Well, Phil I can't be sure this is the episode you're talking about, but in epsidode 361, the only actors I can remember appearing were Grayson and Nancy. There was also the voice of Dr. Woodard, but he didn't appear physically, and Nancy Barrett in fact only shows up briefly, IIRC. Most of the time it was Grayson on screen; and if you're a fan of hers, her performance in the episode is a tour-de-force.
[spoiler]Mostly the episode concerns Julia being tormented by the vengeful ghost of her old friend Dr. Dave Woodard. In actuality though, I think it's really Barnabas using his supernatural powers to "gaslight" Julia into believing the ghost of Woodard is out to get her, because Barnabas is afraid that Julia's going to spill the beans on him, since she is really guilt ridden over her role in Woodard's murder.[/spoiler]
Maybe someone else knows of an episode other than this one that featured only Grayson and Nancy, or knows the background on whether the small number of actors onscreen for this episode had anything to do with DC being pissed about having too many actors in a previous episode.