It turns out all of these messages are related to the same tape drive. I'm relieved to know that it was not something more serious but at the same time wonder why it is TSM could not tell something was happening there and take it offline itself.
12/20/04 08:36:54 ANR8381E 3590 volume U03841 could not be mounted in drive RMT6 (/dev/rmt6). Geoff Gill TSM Administrator NT Systems Support Engineer SAIC E-Mail: [EMAIL PROTECTED] Phone: (858) 826-4062 Pager: (877) 854-0975