I had DISA problems in previous Freeepbx versions but it was solved more or less. Now it seems it is back again with the latest 2.3.
I use Trixbox 2.2 and upgraded to FreePBX 2.3 I use DISA as no. 5 in my IVR and 55 as the pin code.
I simply get a busy tone after pressing the # key. I use this feature from time to time and it is a bit ammoying that it doesn’t work stable as of yet.