DarkBlizz

I had this same problem. Look under your SCII directory, the in the Battle.Net folder. (C:\Program Files\StarCraft II\Battle.net). You should have 2 files: Battle.net.MPQ, and Battle.net-patch.MPQ. If you are missing one of those, then replace it with the one in the original Battle.Net folder, which (If you really did follow directions) you should of backed-up before you deleted. If you did not back up the battle.net folder you deleted, then you MIGHT be able to find the two files in C:\Documents and Settings\All Users\Application Data\Blizzard Entertainment\Battle.net; that is, if your using XP.

In the game lobby on the right-hand side under settings, change the category to the LAST option. Its all in Chinese but it is the LAST and the LONGEST word in the category drop menu. Do this before you invite your friend. 

When I play vs AI or creating a custom game, the map menu is loading infinitely. I have tried re-downloading the map cache, but I still get the same error. Every now and then the maps will load but most of the time its loading forever...Any suggestions?