Channel Unavailable for Dial

Hi All,

I am using Asterisk 1.2.10 , Zaptel 1.2.11 with Te410p card on RHEL4.4 connected with 4 E1 Pri

We use this setup for Auto Dial outs. The problem i have is when the call files are increased in the outgoing folder (but less then the available channels), most of the calls fail showing me "channel unavailable " on the cli prompt. i also tried to use the Zap/g1/xxxxxxxx option.

What could be the reason for this, is it a know issue?