Issue with scrolling credits

I've exported scrolling credits from Premiere Pro and everything was great. I've had to come in to make some revisions, but now when I hit export the credits are no longer scrolling - what I get is just a video clip the length of my credits, but nothing is scrolling. It exports just the frame that the cursor is at i.e. just a black screen if the cursor is at the beginning, or a single page of text if it's half way through the scroll.

I've had them scrolling before and successfully exported, so I'm pretty sure it's a straight-forward fix, but I just don't know what it is!

What things should I be checking? What (if anything) should be selected when I go to export? I'm new to Premiere, so all the things I need to check and remember here would be much appreciated! Thanks folks.