This looks like the famous "cartridge stuck in drive" error.  You might
look and see if there is a cartridge in the drive.  We've seen lots of this
this week on those robots for some reason.  ADSM thinks the drive is
unloaded but it isn't and it comes along and tries to hang another tape on
that drive and can't.  Thus the error message.

I think there were some bad drives as well as a firmware fix that might
help.

Kelly