Blank notification/warning dialog

I have a course built that includes eight quizzes, each of which acts as a gatekeeper to the following section. The setup is such that users have to pass the quiz to continue...if they attempt to click past, a dialog box with an OK button appears, but there is no text in the dialog and I can't figure out why the text doesn't appear (it may just not be specified) or what the dialog is called. Would anyone tell me what to look for in the player template so I can add some sort of text to the dialog? Thanks!