HI,
CNAT_BLOCKIP ....... 1
CNAT_BLOCKPORT ..... 1
These two lines means the IP (the computer is using on the LAN) and the port (16402) that the SIP part of the Invite Process (The bit behind the scenes after the Buddy accepts the Visible part of the invite that creates the failure logs) are Blocked.
The /Applications/iChat.app/Contents/MacOS/iChat -errorLogLevel 7 thing creates of a log of what it "sees" on a "right here, right Now" sort of basis.
It may get different results when connected to another router.
There are some routers that are what is called SIP ready.
They work to enable Landline phones to be used over the Internet using VoIP (Voice over IP) which uses the same SIP connection process iChat and Messages do.
There are also add-on adaptors that can do the same thing the best known are from Vonage.
These also "convert" landline phones to VoIP.
However the process can get messed up. The router or the Vonage device thinks SIP should go to the Phone and "Strips" it out and it never get to the computer doing iChat.
Thomson-Alcatel modems (that route) were like this. They worked in Firmware ver 3 but later versions did not work.
http://www.ralphjohns.co.uk/page4a.html#_text
It is difficult to know what you should do next.
8:41 PM Friday; August 31, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously