Can't move endpoint on the time line in Storyline

I know this is a fairly old thread, but I thought it might be helpful to anyone who found it in the future if I let people know what worked for me in this case (couldn't move timeline endpoint). 

I, too, originally had a longer piece of audio on the timeline and then replaced it with a shorter one (original was 140 seconds long and new one was about 60 seconds).  I didn't have any empty objects on the timeline, and everything was set to run until the timeline's end; but I couldn't drag the endpoint left from 140 seconds.

I finally figured out that there were three objects (a couple of hotspots and a "click each image" textbox that appeared at the very end of the timeline.  When I right-clicked on them and chose "Timing," I found that they all had Start times that were later than the end of my audio (135 seconds with a "Show until end of slide" property).  Once I changed their start times to earlier than the end of the audio (55 seconds), I was able to drag the endpoint left to meet up with the end of the audio.