Random Got SIP response 400 "Bad Request" back from Polycom

I know this is probably an Asterisk issue and I will post there as well, but I get more help here usually…Anyway, I have recently upgraded to Asterisk 1.8.5 and FPBX 2.9 on one of my client systems. They have Polycom phones with firmware: 3.17. Since doing so, I randomly get:

chan_sip.c: – Got SIP response 400 “Bad Request” back from

back from one of the phones when we try to transfer to it. It is random, and seems to only be that phone to this point. It happened to more phones until I upgraded from firmware 3.16 to 3.17. Now it is only that one phone. Any ideas would be much appreciated.

Polycom firmware is up to revision 3.3.1f now… I suggest you upgrade to the 3.2.5 version. Have you upgraded the BootRom too?

The 3.3 and newer version use new configuration file system so upgrading all the way up could be a little more involed.