Electronic Arts UK Community Forums have word from Barrie "Bazajaytee" Tingle that a server fix is inbound for a problem that can cause players to be immediately kicked after joining Battlefield: Bad Company 2 servers (thanks littleme). Here's word:

For all the players connecting to servers and being kicked straight away (and pbsetup.exe or manual updating didn't help) then you will be happy to know we are sending out R4 servers to our hosting providers which will hopefully solve this issue.

This is going out to the hosts shortly and then allowing time for them to update you should see connections going back to normal in the next few hours and continuing to spread to all servers during this evening.