[Asterisk-Users] Can't Native Bridge Any More

[Robert DeVries]

I have a number of situations where in the past I would get a native
bridge, IAX to IAX - e.g., call coming in on an IAX VOIP line being
forwarded to PSTN via another IAX termination provider, or calls made
from my IAXY to a PSTN number via my Asterisk box to a VOIP provider. 
I find the native bridge desirable because it removes at least one hop
from the call.

For the last few week, no native bridging under any circumstances.  I
get a message on the console that "attempting native bridge", then a
message that it is "unable to transfer.

I don't believe that I have made any changes that should have cause
this, and, in particular, I haven't added any "notransfer" statements.

Any ideas?