Ok, just figured it out. I had to go and open and select the file from the backup folder. I had thought it would just automatically open the latest but I guess when you move from one computer to the other it's just a bit different... thanks for your time.
No, that doesn't sound right. When I move to my second computer it's just like I plugged back into the first. I'm a bit slow today, so all I can think of is
1) have you got your "Database Previews.lrdata" on the portable hard drive with your catalog?
2) Are you sure you are opening the catalog on the portable hard drive? (preferences/general/default catalog: prompt me when starting Lightroom). David