Got reject for frame , retransmitting zt_pri_error problem

Hi,

Recently we changed our pri provider and they asked from us to enable echo cancellation.
We have asterisk (1.4.21) with digium E1 TE205P, but without hardware echo cancellation - so we enable the soft - and many times (for outbound calls) - the agents receives the message that the number is busy - but that is not true - and another times echo in the line.

log files:
Many Messages of "zaptel Disabled echo canceller because of tone (rx)"
and after sometime:
“timing source auto card 0!
wct2xxp: Clearing yellow alarm on span 1
Zaptel: Master changed to TE2/0/1
wct2xxp: Clearing yellow alarm on span 2”

Any idea ?