Seems to have been covered elsewhere, but not quite the same issue.
Updated to latest verison of Snow Leopard on my MacBook Pro and Mac Pro in preparation for installing Lion.
Installed Lion on MBP which all went perfectly and been using it for a week without problem. So, time to install on the Mac Pro.
First, installed it on a blank external disk connected to Mac Pro, as an emergency disk. At the end the MP would boot from that drive and I could log in with the single admin account that I had created. Looking good so far.
Rebooted into SL and installed Lion again, but on the main disc. No errors and was finally presented with the login screen, listing all the correct users. Selected a mobile user account (account is on local SL server) and I was able to type in the password, but then when pressing return (or clicking arrow on RHS of text box) the arrow is replaced with a spinning daisy wheel which spins forever.
Logged in remotely (which works fine) and rebooted machine. Tried to login with a local admin account, but same problem. I can however login in with the Guest account, but if I try to switch users to another more useful account, it's just a big grey blank screen.
So there is something up with Lion being able to log in to those existing accounts.
I tried to boot into safe mode (from the main HD), I get the progress bar which seems to be Lion's way of saying it's starting in safe mode, but then a while after the progress bar completes and vanishes, it reboots all by itself. If i just let it boot and try and login, I'm stuck again (it's obviously NOT in safe mode) and if I hold down shift again while rebooting, I get the progress bar and eventually another auto reboot and so on. IOW, it is NOT possible to fully safe boot.
Since the MBP contained the exact same accounts and it was bouind to the same server when it was upgraded, I cannot understand why it's such a problem on the MP, yet working perfectly on the MBP. Anyone shed any light on this?