Project won't build

A project I’ve been working on all day suddenly stopped building. Every time I try to build it, it gets stuck here:

I’ve restarted the computer and also cleared the App Builder folder in my Temp directory. Any other ideas of what is preventing this from building?

Other apps build fine. It seems like it’s just this one.

If you are using SAB 10.2, you can go to the Tools > View Logs menu item which displays a dialog with the Error log and Output log. Is there anything displayed in the Error log?

No, sorry I had looked there but forgot to post that in the original message.