My Book for Mac - not working with Time Machine

Hi, I recently moved back to the UK from Japan, where I bought My Book as a hard drive for iMac to back up the data using Time Machine.  It worked fine there, but back in the UK i get an error message ‘Time Machine could not complete the backup.  The backup disc is not available.’  However, my book is plugged into the iMac and it is connected to the power socket.  I haven’t changed the power lead - its just plugged into the socket using a basic adaptor.  But the front light on the My Book is flashing a few times a second which I undersand means it is powered ok.  I wondered if anyone could please help suggest some actions I could take?

Aside from the time machine error, can you access the my book fine? Also check if you have the latest firmware update.