it is most likely a codec that is setup in the SIP trunk. It will not harm you but is a nuisance.
check what you have in there and if g.723 and maybe g.711a are in there toss them out then try again.
If the error comes back maybe the trunk has trouble also with g.722
Joe
FHandw, ACSS, ACIS
"Dew knot truss yore Spell Cheque