FileVault 2 Error: -69755

I have recently installed a Seagate Momentus XT 750gb hybrid drive into my new MacBook Pro. It was installed as a new drive with Lion, then upgraded to ML, and Time Machine was used to restore some files only, so not a full system restore.

I have been very impressed with the performance of the hybrid drive for things like booting because of the way it uses its 4gb SSD area, and I decided yesterday to enable FileVault to increase security. I performed Verify's in Disk Utility first then started the encyrption process which seemed fine. I even kept using the system and at one point rebooted and was presented with the FileVault logon screen at bootup displaying the enabled users as it should have, and I logged in without issue.

I left the system running overnight to complete the encryption process (which it was reporting would take 9 hours) and I had a message this morning saying that there was a problem with the encryption process and I should remove FileVault. When I go into Security & Privacy in System Preferences it immediately gives me a window titled 'There was a problem enabling FileVault' and the message 'Problems were encountered with the disk “MacBook Pro”. Please turn off FileVault, verify and (if necessary) repair the disk with Disk Utility, and try enabling FileVault again.' with a button to 'Turn Off FileVault...'. When I try to do this it asks for the local admin password then thinks about it for about 30 seconds, asks me to confirm I want to disable FileVault, then immediately gives me a new window titled 'Disabling FileVault Failed' with the message 'An error occurred while reverting the disk. (Error: -69755)' and immediately returns to the first warning of the problem again, and this just goes around in circles.

When I reboot I no longer have the FileVault logon screen and it just runs as if FileVault is not turned on, but when I'm back in ML and bring up the disk info it still claims to be encrypted. If I reboot to the recovery partition and run disk utility it will not allow me to mount the drive.

This one has thrown me. System performance is fine, all data is there, running a disk verify and permissions verify both come up clean, but obviously FileVault is not doing its job properly and I'm not sure what the problem could be. I would prefer get FileVault working properly rather than remove it. I have a Time Machine backup so I have all data backed up in case it starts to flip out, but any suggestions will be gratefully received.