Can't open Quizmaker file in Storyline

When I try to import a presenter file into Storyline that includes quizzes and engage interactions, the quizzes and EIs won't import. The error says "couldn't open Quizmaker file. A quiz being imported is in use by another application. Please close any other applications...". But there is no way the quiz is open by anyone anywhere else. Can you think of another reason this error message might be coming up?