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alex, you need to rewire the switch and disable it to use 1MB bank on the duo, it can be done however.
I meant you can build a 1MB BIOS and flash both banks at once (512k per bank), but it's better to flash one bank at a time in case of unforeseen errors (like what he just did).
Oops... accidentally edited your post insteading of creating a reply. D'oh.