joseuro:
so I use an external power supply, connected to the 5v from usb using wires and powering the cartridge directly with it.
Ok then it's not a power supply problem either. The N64 carts need a good 3.3V supply, for example I tried with a power supply that only gave me 3.2V and I got errors too. But that external supply you're using looks good enough for the job.
If the info screen isn't correct it can't read the cart at all and it won't dump right, neither rom nor save.
Maybe it really is just that the wires are too long. It is known in the N64 portable scene that long wires on the cartridge port make the N64 malfunctioning. But this will fix itself after you receive my pcb set 
MichlK:
Truely impressive, what all you guys did here - it is hardly comparable to the tiny project I published three years ago
Thanks, open source is a really powerful thing 