Invite problem?

Hey guys, so yesterday and today my friends and I have been running into a few issues, and have tried to troubleshoot them ourselves, but obviously that has not worked. I had my friend over Friday, and he signed into my laptop so we could play together and I could teach him the ropes of the game. It all worked fine and as intended and I was able to show him the game. Then, today he was on his own computer and we were trying to play together, but we can't send invites to each other. We have tried many ways around this, such as having another friend invite us both to a lobby, but when both of us are invited, one of us can't join. It feels as if the game just does not want us to play together :P. Please note, my friend can get into my other friends lobby. I can get into my other friends lobby. But we cannot whatsoever get into the same lobby together. Any Ideas?