Upgrading my Netgear DGN 1000 with custom firmware?

I have a Netgear DGN 1000 router and I want to upgrade its firmware. If I upgrade using the original firmware, it's okay. But I have modified the original firmware, because of a "short-range" bug in MIMO technology.
However when I try to upload it to the router it gives me the error saying that my upgrade file is not the right version nor type for this router and that I have to get the right file, then try again.
