I have an iPod that is not detected on Macbook Air 11

Hi!

This is very strange, I have an iPod that is not detected on Macbook Air 11 (but the battery icon switches to 'charging') unless I connect it through an unpowered USB hub.

I tried a lot of things:

1) use a different cable on my macbook air (ipod not detected, battery icon switches to 'charging')

2) try those cables with another ipod on my macbook air (new ipod was detected)

3) try the ipod on a windows machine (ipod detected)

4) try the ipod on my macbook air through a USB hub with no external power (ipod detected)

5) Soft reset and repeat everything, same result.

6) Restore ipod on another mac and repeat everything, same result.

Everything on this ipod is working fine. I though that it may be something related with the USB ports on my mac, but other devices and other ipods work fine too. Any ideas?

Thanks for your help!