Trouble with Meetme - Call cannot be completed as dialed

I need some help with the conference feature. When I dial 2663, I get “Your call cannot be completed as dialed.”

In the log I found: “app_meetme.c: Unable to write frame to channel”.

Can you give me some tips on how to resolve this? I am struggling a bit on how conferencing is supposed to work. Is this a configuration problem? Am I missing a module? I appreciate any help you can provide.

I am running PIAF 1.7.5.7.1, FreePBX 2.9.0.7. I am using the Nortel 1535 (Turkish).

Thanks.

Do you have dahdi setup and configured. Meetme requires dahdi loaded in asterisk.