Can't modify media with lync client

Hi All

I've tried to modify media with lync client after call is connected. but i got 500 response from lync client.

does lync client support modify media during a call?

eg. make call from our ipphone to lync client, call established with codec RTA/16000.

then i send a re-invite with codce G.711 A-Law only, lync client response a 500 "internal server error" to me. and i check the OCSlog, it says "codec not supported"

thanks.

oyjcq