It's possible it's an issue with the signal option not being set (Japanese GCNs output a different signal than UK or NTSC GCNs and this will need to be set in your devices settings. It's the list of settings that is like NTSC_M, NTSC_433, PAL_B, etc.

Do you have any other SD console you can test? Maybe a US or UK GCN?

Also, are you using RECentral or LGP Stream Engine as a source?

If I remember right GCN's AV cable is component, right? Did you make sure to switch to component in REcentral / Stream engine?

It's better using a SD capture. I use a GV-USB2

Avermedia doesnt take Composite Video (Yellow Cable), you need Component (Red Green Blue).

That's strange...

I play my RE2 (USA-version) on a chipped japanese Gamecube, and my Elgato HD have no problem grabbing the signal. Hope you'll find a solution.

EDIT: Oh yeah, and I only use AV-cables.