Charging Not Supported with USB Extension Cable

Hi,

I have a 3GS, and I want to extend the short usb charging cable that comes with the charging block. I bought a USB extension cable, but when I plug that in to the charger, then the Apple cable to the extension, and the Apple cable to the phone, the phone displays an error message indicating that charging is not supported with this accessory.

Is there something special I'm missing here?

Thanks.

it must be an issue with the type of USB extension cable you have. I have used 2 different USB extension cables, (both 6ft long) on 2 different charging blocks, one was the stock apple block and the other was a 3rd party model. and they all work fine for charging and syncing

my USB extension cables are pretty old, I got them around 2000 / 2001