Do you have the file called UPDATE.ZIP ? And is it the correct file from Envizen for your tablet? I would contact them to make sure. The OS updater service is looking for the file and for some reason can't locate it. It needs to be on the system on the main flash storage (NAND) or SD Card.
You also need enough space on the NAND for it to expand. You may need to delete or copy off as much stuff as you can (i.e. pictures, games or books). Frankly I would make a full backup externally to be sure I don't loose anything.