I've had thise several times, coincidentally after something has been done by Virgin in the house ! If like me you haven't changed any settings since it used to work (I have an automated upload every 30 secs) the you need to make this quite clear to Virgin Support. Basically, they have a problem with security on one or more of their servers.
Also, as you can see from my homepage below, there is a dot in my username !
http://homepage.ntlworld.com/sutton....rweb/index.htm