asterisk users - Aug 2011 - Unable to enable echo cancellation on channel 1 (No such device)

Hi All;

Suddenly, we restarted the Asterisk machine and the echo appeared. The lines are
analoge.

At the consol, I see this message:

[Aug 10 14:36:05] WARNING[3789]: chan_dahdi.c:4831 dahdi_enable_ec: Unable to
enable echo cancellation on channel 1 (No such device)
[Aug 10 14:36:07] WARNING[3789]: chan_dahdi.c:4831 dahdi_enable_ec: Unable to
enable echo cancellation on channel 1 (No such device)

What could be the reason?

The asterisk version is Asterisk 1.8.5.0
DAHDI Version: 2.4.1.2 Echo Canceller

At the system.conf I have the following:

echocanceller=mg2,1-16
fxoks=1-16


At the chan_dahdi.conf

context=IncomingPSTN
signalling=fxs_ks
rxgain=0.0
txgain=0.0
channel => 1-16

group=1
channel => 1-16

The calls are working, but the echo is appearing.
Something strange is the result of the dahd_cfg, but really if I changed the
configuration in the system.conf and I made it fxs instead of fxo, then it is
not working:

[root at PBX-FF asterisk]# dahdi_cfg
DAHDI_CHANCONFIG failed on channel 1: Invalid argument (22)
Selected signaling not supported
Possible causes:
        FXO signaling is being used on a FXO interface (use a FXS signaling
variant)
        RBS signaling is being used on a E1 CCS span
        Signaling is being assigned to channel 16 of an E1 CAS span
[root at PBX-FF asterisk]#

Any help?
Maybe the version I have has a bug?
Or I have to do recompilation?

Regards
Bilal