Try putting flash in your PC and let it checkdisk. That may not get your disk assignments back, but it might fix something.
While you have it in your PC, make a backup. You should always have a current backup of flash. All of your settings you made in the webUI are stored in the config folder on flash. As long as you have that, you can always restore that config folder to a new install and you will be going again. Any time you make any significant changes to your settings you should get a backup of flash. This is especially important if you make any changes to disk assignments (add, replace, remove).
You can always download a zipped copy of flash at Main - Boot Device - Flash - Flash Backup.
After you get that backup made on your PC, try again, and if necessary, reassign disks.