I'm having the same problem. The other day if I shut down BFBC and restarted it work ok but now I log in ok but after selecting a server it ask me to check my connection, which is fine. What did you do to fix it?
It's maybe late for answer but apparently this problem still occuring for some people as like me.
In steam version (which I have), open game properties by right clicking on Bad Company 2 in the library and then click "Set Launch Options".
In this box, type "-pinginterval 50000" without quatation marks ofcourse and click OK. That's it. This launch setting solved my "connection problem" issue.
