Theatre on Cable TV in 1980's

Had a question regarding a play I saw as a child on cable television in the 1980s. It was a play within a play. In the middle of the play somehow an actor had said the wrong line, and the play had to be re-written from that point forward, and all the actors had to learn new lines.

I remember the set had the audience painted upstage, and the actors performed the play-within-a-play upstage. the viewer was seeing the play as if from backstage looking out to the audience. It may have been on Showtime or HBO. Would you have any idea what play I am talking about?

FYI, it is not Noises Off.

Could it be this?

http://www.imdb.com/title/tt0274854/

Sorry, it's not Six Characters in Search of an Author.

was on Showtime

Footlight Frenzy

http://www.samuelfrench.com/p/5257/footlight-frenzy