install of 5.1.0 and 5.0.1 fails

I was using calibre 4.23.0 on Ubuntu 16.04. Got an update message for 5.0.1, which I didn't have time to install. Then got an update message for 5.1.0 and tried to install it using the command prompt. It appeared to work but when I ran calibre, the icon flashed a few times, then disappeared and I got a message that Ubuntu had experienced an error. So I tried uninstalling 5.1.0 and installing 5.0.1 and the same thing happened - install appeared to work but calibre wouldn't run. So, I've rolled back to 4.23.0 and calibre appears to be working.