i use inadyn with DM800 - no problem
although i run enigma2 :-)
make sure
INADYN_USERNAME=
is the username you use to login to the dyndns site
also change the update period
#UPDATE_PERIOD=60000
UPDATE_PERIOD=1800000
and
DYN_SYSTEM_ON=1
DYN_SYSTEM=dyndns@dyndns.org