Thanks guys for the reply...
The mouse is powered via the USB connection...
Just as an update... I did a system restore back to the 6th Dec before the last batch of Windows updates. That didn't solve the problem! Have downloaded the latest software update for the mouse... Problem is intermittent so I wont know if its fixed for a while... or at least until it happens again!
Would be nice if one could contact photobucket to report the problem but all there appears to be is pages of Knowledge Base type material, none of which seem particularly relevant... ah well....