Look at my configuration please:
#cat /usr/tivoli/tsm/client/api/bin/dsm.sys
   SErvername             TSMSERVER
   COMMMethod         TCPip
   TCPPort                  1500
   TCPServeraddress   10.0.65.20
   nodename               testlpar

# cat /usr/tivoli/tsm/client/api/bin/dsm.sys
SErvername         TSMSERVER

# su - db2inst1
# cd sqllib/adm
# dump -HX64 db2sysc
db2sysc:
dump: db2sysc: 0654-108 file is not valid in the current object file mode.
        Use the -X option to specify the desired object mode.

So, my instance is 32-bit.

# exit
# whoami
root
# /usr/opt/db2_08_01/adsm/dsmapipw
Your new password has been accepted and updated.
# su - db2inst
# set | grep DSM
DSMI_CONFIG=/usr/tivoli/tsm/client/api/bin/dsm.opt
DSMI_DIR=/usr/tivoli/tsm/client/api/bin
DSMI_LOG=/home/db2inst1/dsmilog.log

# db2stop
# db2start
# db2 backup db mydb use tsm
SQL2062N  An error occurred while accessing media
"/home/db2inst1/sqllib/adsm/libtsm.a".  Reason code: "959".

What do you think the problem is?
Regards,
Mehdi