Get your mates to go to 'Game Data Utility' and delete everything that has MW2 in it. They don't need patch blocker, just tell them to go to Network Settings > Internet Connection Settings > Custom > Wired or Wireless > Manual > Go Across To Proxy Settings > Go 'Use Proxy' > Type In 210.101.131.231 > It works without a patch blocker.
---------- Post added at 08:47 PM ---------- Previous post was at 08:46 PM ----------
They will now be able to join you!