this seems to be happening more lately. First if this happens the only thing we have found that helps is to reset or power-cycle your router. If you're not using a router you'll have to call your ISP and see if they blocked any ports.
Now this is really important. If you fail to patch and your IM is not updated DO NOT buy anything from it. This can cause an error in your data and make that character corrupt. As far as i've heard this cannot be recovered.
sorry i don't have a definitive fix for you but I'll let you know any progress i hear on this problem.