I have the same problem here.
I am using also Axon 1.30 with IVM 4.01.
Here is my log file:
22:45:19 Call sip:7175886@trickiegi.nl -> 002
22:45:23 Call sip:7175886@trickiegi.nl -> 002 answered
22:45:56 LSipCall::SendReInviteAndWaitForFinalResponse
22:45:57 LSipCall::SendReInviteAndWaitForFinalResponse uInviteResponse: 200
22:45:57 LPBXSipLine::Reinvite uInviteResponse: 200
22:45:57 Error returned: 400 Bad request
22:45:57 Call sip:7175886@trickiegi.nl -> 002 disconnected
Extension 002 is IVM.
I get the error when IVM is trying to doing a blind transfer to an external line number.
When i do the same transfer to an internal extension i do not get "22:45:57 Error returned: 400 Bad request"
I hope somebody can help me with this information.