Dahdi 2.6 is currenlty not working with Wanpipe 3.5.24, please use Dahdi 2.5.0.2 or lower. URL's are below for the most recently supported Dahdi version as well as where all Dahdi releases are stored. 

This Issue will be resolved shortly in the 3.5.25 release of Wanpipe. 

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Dahdi 2.5.0.2 Complete Package - http://downloads.asterisk.org/pub/telephony/dahdi-linux-complete/releases/dahdi-linux-complete-2.5.0.2+2.5.0.2.tar.gz

Dahdi Releases - http://downloads.asterisk.org/pub/telephony/dahdi-linux-complete/releases/