Asterisk, Digium TE121B on E1/R2 line setup

Hello all,

we would like to ask for your assistance.
here is our setup:

Redhat 5.2
Asterisk 1.6 (OpenR2 patched from http://svn.digium.com/svn/asterisk/team/moy/mfcr2)
DAHDI linux 2.1.0.4
DAHDI tools 2.1.0.2
OpenR2-1.1.0

Hardware: Digium TE121B
Digital line: E1/R2

/etc/dahdi/system.conf
span=1,1,0,cas,hdb3
cas=1-15:1101
dchan=16
cas=17-31:1101
loadzone=ph
defaultzone-ph

we followed the guide "openr2-guide-0.1.pdf"
from http://code.google.com/p/openr2/downloads/list

we also plug a loopback cable (shorting pin 1 and 4, pin 2 and 5) on the digium card
and we got a green LED. the test commands has no error outputs.
but  when inserting the E1/R2 line, we always get a red LED.

we have read that with only DAHDI running and the configuration
of system.conf above, we should be able to get a green LED.

is there a problem with our setup or at the telco's side?
if you have this experienced please share and advise.

Thank you very much.