Not sure what happened, but all of my actions to send MSN messages now fail with build 6.3.0.1855 (I think they also failed with 6.3.0.1816) [I've noticed this within the last 60 days or so]
I can use my MSN client and connect using the information placed in the MSN Actions, so I know it isn't invalid data - it just appears that the action no longer functions. Maybe Microsoft changed something so the code in the action won't connect any more?
I seems Microsoft has turned off support for older protocol versions recently. We found a derivative of the library we use that now supports the newer protocol versions, so we should have a fix for this early next week (we got a test console app working late on friday afternoon).