This is the reason you need to upgrade to WooshBuild v5.
OpenATV have released an update which if run on boxes with image made around the same time as WoohBuild v4, will cause the box not to boot. Their only fix, as it is not actually OpenATV's fault is to reflash your box wih a newer version of OpenATV. WooshBuild v5 is not effected by this software update and works fine.
A WooshBuild newsletter was sent out and also posts have been made in the v4 and v5 support threads.
You only option now it to flash your box. Flash BaseBuild from a spare USB stick and then follow the instructions. When asked if it is OK to delete existing data from you main USB device, say NO.
Because you cannot make a settings backup, you will also need to find your line details as they will need adding.
Follow the instructions for installig WooshBuild v5 and you can't really go wrong.
Some images have already been remade due to this issue but v5 avoided it by chance and timing.