When attempting to install the beta, I had inadequate space on / and /usr.
The install progresed until the point where it checked space, then poped up
the dialog. I hit back once or twice, then got an error dialog box. This
was reproducable (I had several partitions I had to make room on). I did
not save the error messages (I was doing several things at the time and it
was quite late).
I believe this has been fixed since the beta - needs to be verified by QA.
I have verified this as fixed. The back button takes you to the previous screen
as it should.