Same here - I also had a lot of problems with file transfers.
Symptom: Locking chat window, unable to type. Close chat window and re-open conversation and was OK. Many problems with file transfer stalling. Almost fixed now UPNP is enabled on firewall(s).
MSN diagnosis Shows wireless LAN with cascaded UPnP port-restricted NAT router
Plugins: clipboard transfer script
Version: MSGPlusLive 4.2.1
MSN Messenger Live: 8.1 build 8.1.0178.00
Host OS: XP Pro SP2 - Build 2600 - Updates 100% as of 24/05/2007
CPU: Dual Intel T2080 @ 1.73Ghz , 0.99Gb RAM, 120gb HDD
AV Software: AVG 7.5.476
Firewall: ZoneAlarm Free:
ZoneAlarm version:7.0.337.000
TrueVector version:7.0.337.000
Driver version:7.0.337.000
Have uninstalled MSNP and it seems okay so far