From comments on the forum over the years, the project itself on the timeline must be less than 2 minutes (i.e. 2 minutes less one frame at a maximum) with nothing else on the timeline after the end point such as a marker. Some have reported that they've attempted - unsuccessfully - to render an under 2 minutes section of a, say, 10 minutes project in a trial version.

Given the pop-up, it may be that the project on the timeline is longer than 2 minutes less one frame or there's something else on the timeline at the 2 minutes point or later.