I, too have two boxes and came across this problem on one of them a couple of days ago; tried everything, but couldn't get the write-back to work. Today I had to update the EPG on the other box and thought I was going to lose that one, too; much to my surprise, it worked perfectly! So then I switched USBs, did the same thing and that worked, too! I transferred the USB to my secobd drive and now I've got working EPG on both...
If bigback is right and someone's trying to force us to pay (it's called blackmail), then that situation might not last, of course. In the meantime and for what it's worth, the only difference between the two boxes is that the one that's still working has latest (?) Skybox.cc firmware, while the other has Openbox's own (don't have versions to hand, but I can dig them out if relevant)
By the way, if it IS blackmail, then I certainly won't be paying!