I put a new 256 MB card in the G2X and now it records data without any problem.
But, it still doesn't explain why it doesn't work with a 4 GB card, tried with 2 different, brand new...
Thanks for your help.
When the black G2X came out, i don't think 4GB cards were readily available. Its too much of an expansion. On one of my old laptops, you can't have too big of a USB thumb drive without updating the Windows I think. Another example would be trying to fit a newer TB hard drive on an old motherboard that only supported a couple gigs at the most. The electronics just aren't compatible.