Hi, I have answered a few similar questions about format error. sometimes when you try to format the USB flash drive the Window won't let you format or indicates like "the drive is not formatted, would you like to format it now?" or so. We called such kind problem as "format error". The possible reasons may vary, your flash drive may corrupt or crashed or meet kind of physical damage, or there are internal problem when the drive is manufactured.
As to the solution, I'll suggest you recover the data in your flash drive with a format recovery
program in the first hand. Then send the drive to a special shop or directly to the manufacturer. Programs like Recuva or Wondershare Data Recovery may recover the data. Regards