Transfer gets hangup request, cause 16

I have Asterisk 1.4.33 in between a Merlin Legend and the outside world.

Phone Co. <–PRI–> Asterisk <–PRI–> Merlin Legend

I just switched to DAHDI from Zaptel

When a call transfers from our incoming PRI to Asterisk to our Merlin Legend (via PRI) the call drops when it is transferred from the ringing phone to voicemail (on the Legend). I get the message:

Channel 0/23, span 2 got hangup request, cause 16

I saw an article at which says to change “transfer=yes” to “transfer=no” in:
This actually made it worse! I had no problems when using Zaptel. DAHDI is killing me! Any ideas?