your drive is LTO2, so you're OK with LTO2 tapes. Your drive and path configuration is all fine, and the drive was definitely available.
Let's have a "q node <nodename> f=d" on the node you're trying to retrieve as, with particular attention to the " Maximum Mount Points Allowed:" value. It is entirely possible to do backups and archives with that set to zero, as long as everything you're doing can go into DISK class storage. Then, when it's migrated to something sequential, you can't have a mountpoint to get to it. maxnummp isn't supposed to be enforced for read operations, but there are plenty of other bugs, why not that one?
Oh, and of course you most certainly can restore from a readonly volume. I think somebody doesn't know the difference between readonly and unavailable or offsite or destroyed. However, the fact that it is readonly is potentially troublesome. Unless you're doing something like marking them readonly to prevent data from being deleted (that won't work), there has been a problem with that volume. Your data may or may not be ok. I would suggest auditing it, and if nothing is found wrong, mark it back to readwrite. I have had volumes go readonly when there wasn't really a problem - for instance, I was downloading drive logs just last week (for a different library issue), and that caused drive hickups.
