DFU suffix does not match

[user5647]

when trying to upload the firmware, i get 2 messages in the DFU
1st, to connect and hold down both DFU and start ect..
After hitting return, i get the 2nd message "dfu suffix does not match
A valid dfu suffix will be required in a future dfu- until release!!!
Deducing device dfu version from functional descriptor length
Cannot item dfu device 1fc9:000c
No dfu capable USB device available

Press any key to continue"

How do i fix this?

[user5647]

Also, i tried both the most recent version and the previous one

[insidecircuits]

You need to put your board into DFU mode, follow the flashing procedure.