It seems to be due to technical hitches because they are installing new software and making changes to the iPlayer, and these are supposedly just teething troubles. The BBC have indicated that their intention is not to bar non-UK listeners from the radio waves. There's an informative thread on the BBC forum, and their moderator is trying to find out more info and keep the board informed. The thread is here:

http://www.bbc.co.uk/dna/mbradio2/F2142825?thread=5660968