I've followed the instructions: Attention: instant messaging model has changed from 4.7 to 5.0 dramatically and in a non-standard way. 5.0 takes session establishement using INVITE and drops out-of-dialog MESSAGEs on the floor, whereas sending "481 Call Leg/Transaction...". To permit them, apply the following registry setting: HighSecurityMode HKLM\Software\Policies\Microsoft\Messenger\Client{83D4679F-B6D7-11D2-BF36-0 0C04FB90A03}_Default\EnableSIPHighSecurityMode DWORD= 0 -- Low Security 1 -- High Security 2(Default, same as not set) --- Medium security You need set it to 0 in order to make peer-to-peer IM. Since WM4.7 client is not registered in the LCS server, I guess that WM5 treats it as peer-to-peer call. And I'm still getting the following error: <<messenger5dump>>

Any ideas?

--joe