I'm having the exact same problem and have had ever since I upgraded my msn to v. 8.1 ... grrrrrrrrr
I'm getting very fed up. It starts out where every third or fourth message won't go through giving me the very same message as in your screen shot. Then after a while I may get one or two messages through in a row after eight or more "could not be delivered" error messages .. then finally ... none of my messages can be delivered. Yet, folks can message me just fine.
If this was a firewall issue it would happen always ... it is intermittent, everything will be fine for several days and then (gee usually weekends) poof .. I am stuck copy/pasting my message over and over and over until it finally goes through .. if ever.
It's extremely frustrating as I do much of my business on line with messenger .... I am strongly considering changing to another service and have no desire to upgrade any further as every time I do upgrade some issue causes me problems.
Is there anyone from msn monitoring these forums who could provide us with some answers ... even an "I don't know" or "Its a known problem, but we are looking into it" would please me .... perhaps even some fix we could utilize? something to say you all care about your customers would be nice ... can ya tell I've been dealing with this problem for so long I'm spitting nails ..
At least I'm glad to see it isn't just me.