time machine hanging

[Moving this from an incorrect 10.5 discussion location]

My new Macbook air, mid 2011 i7 running 10.7.1 with an OWC 360GB SSD, hangs after an hour of time machine back up when backing up to a directly connected external usb drive. The drive is a brand new SansDigital TowerStor TS2CT with 2TB x2 drives. At first I thought the new drive was the problem, but it works fine as a time machine disk for my MBP running 10.7.1.

When it hangs the time machine indicator is turning and the menu is active at first but when I start clicking on things I rapidly get a SBOD and no apps launch. No force quite either so hard reboot is the only way out.

Anyone else having time machine hangs?

Also,

I've just discovered that I can not back up to usb disks attached to a airport extreme. My MBA finds the disk and will allow me to set that express usb disk as the destination but as soon as it tries to start the backup, I get an error stating that the disk is not available--even though it is mounted and time machine sees it. I know that usb drives on an extreme as time machine disks are not officially supported but this has always worked for me and is working for all my other machines, including an iMac and a MBP all running 10.7.1.

Do I need to reinstall LION or are others having this problem?

Thanks