Can't drag everything on Timeline, why?

Yeremyah Posts: 995 Enthusiast

So I have a 40 minute video, but then decided to create a 10 minute intro audio which I now want to add to the beginning of the video.

But when I highlight everything to drag it down 10 minutes, it won't let me, as I drag everything to the right I can see it moving, but then when I let go left mouse button it pops back into the same place.

What am I doing wrong?  How can I drag everything in Video and Audio to the right 10 minutes?

Thank you :)