Time machine is pointing to an external 2TB Seagate USB drive with 1TB partitioned for TM backups. Time machine appears to backup correctly, going through the motions. I look at the time stamp on the sparse bundle and it is in sync with the backups occuring.
When I select "Enter Time Machine" from the menu bar icon nothing happens. Time machine doesn't launch, I don't see a process kick off in Activity Monitor or if I run top in a terminal window.
I would remove the app to see if that fixes the problem but I'm not sure how to restore it if I do.
I've done the Time Machine 'reset' procedure on the Pondini site (thanks) along with running Disk Util to repair the backup disk.
I'm a little stumped on this one. I really hate the idea of completely re-installing Lion.
I figured out what the problem was. When I started using the drive as a Time Machine backup, I just plugged it in without taking a look at the partioning other than size. What I had was a couple of partitions that were both formatted as MSDOS and not with GUID. Although Time Machine will happily write to a MSDOS partitition, it doesn't seem to want to use it when you try and launch time machine.
I had done a couple of successful repairs with no errors so I ruled that out.
I repartitioned the drive, let Time Machine do a backup to the new GUID journaled FS and it worked straight away. I'm sure there is an Apple manual that says make sure you're drive is GUID journaled but I didn't put 2 and 2 together.
All seems happy now.