I modfied the script as follows in order to get it to work:

FROM:

DAHDI=asterisk -rx "zap show channels" | grep -v from-internal | grep -v pseudo | grep -v Language | awk '{print $1}' | head -n 1

TO:

DAHDI=asterisk -rx "dahdi show channels" | grep -v from-internal | grep -v pseudo | grep -v Language | awk '{print $1}' | head -n 1

ALSO--------

FROM:

asterisk -rx "zap show channels" | grep -v from-internal | grep -v pseudo | grep -v Language | awk '{print $1}' | tail -n 2 | while read LINEA

TO:

asterisk -rx "dahdi show channels" | grep -v from-internal | grep -v pseudo | grep -v Language | awk '{print $1}' | tail -n +2 | while read LINEA