It is likely the wrong software in the bv. Pull out (with the power off, everything always with power off when moving hardware in and out) the bill validator and look under it to see if your have a 32 pin removable eprom installed there or a surface mounted flash chip (which would be really thin and flat and not removable). If you have an eprom based unit, a vendor can just sell you a chip and you replace it, if it is flash, then you need to send it somewhere to be flashed, or buy a new transport with the correct software, they are now cheap enough where it doesn't make sense to send it to have it flash and pay the shipping back and forth. Sometimes they put stickers on the chips that I am referring to with the software version installed. There's a chance that you are also missing the rs-232 board for that validator. It would be on the bottom left hand side of the validator, if you are looking at it straight on where the bills go in. The board is flushed against the bottom left side of the transport, if the board is not there, there's a hole and you can see the dbv mainboard through the whole. Post a picture of the dbv's left side and we would be able to tell you right away if you have the needed rs-232 board.