my 7044-44P refuses to boot off a mksysb -i-Tape.

What happens: When I try to boot off a mksysb-Tape the system accesses
the Tape several Times, but doesn't really load. After a long time (~15
min.) it starts displaying that it loads the kernel off the Tape (shows
st and the Drives SCSI ID 2). Then it again takes ~15 min. until I get a
4B27D4C4. However, all Diag-Runs show the system is OK as shows it's
normal day-to-day Operation. There is also NO problem booting off CDROM
or Disk!

What I tried:
The drive is a HP DDS-III Tape which was previously used in a
FreeBSD-Machine. Before I moved the Drive I connected to a Windows-PC
and ran HP-Diagnostics and also checked if the drive was at the latest
Firmware Level (it was - and it was tested w/o Problems). I put it into
the second Media Bay of the 7044 and assigned it SCSI ID 2 (CD-ROM is 1,
the Disk-Drives are 6 and 5).

The Jumpers are set according to the drives manual and the AIX FAQ. I
also checked recent Info on the HP-WebSite which confirmed the Settings
(I use the ones for MRS: On / On / Off / On / On / Off / Off / On). I
checked this several times and even switched all Switches to their
opposite and then back, in case there were contact problems.

When I backup the System to the Drive using mksysb, while I cannot boot
off the Tape, the Backup itself is OK, i.e. I can read it and, after
booting off CD-ROM, I can also restore the whole System w/o any Problems
from that same Tape that refuses to boot.

I, however, was unable to restore a System that was backed up w/o -p
(got an error duing decompression).

I tried this several times, i.e. mksysb -i to multiple Tapes, but the
Problem persists. Btw: After a test-read of the Tape there are no
entries in errpt.

I searched around the AIX FAQ and this Newsgroup but, unfortunately,
didn't find any hint.

Would be nice to get some helpfull hints!