Fans of Megan Mullally and her boozy 'Will & Grace' alter-ego better pour themselves a big Karen Walker-sized glass of vodka before reading this.

In an exclusive interview with AOL TV, Mullally broke the news that her much talked about 'Karen: The Musical' is on hold ... indefinitely. "We had written permission to do the show, and that permission has now been called into question by some powers that be," Mullally explained. "So we may not be able to do it, because we may not have the rights ... which is really sad."

In the midst of a very busy day -- in Oklahoma City, picking up her mom to take her to the eye doctor -- Mullally even took the time to call back to discuss it in more detail, realizing that it's a "sensitive topic." We've held off reporting it so she could let her producing partner and costar in the project, Broadway legend Leslie Jordan (a.k.a. 'W&G''s Beverly Leslie), know. Mullally explained: "I haven't talked to anyone in the press yet because it just happened."