Sharing of network drive not working

Im having trouble accessing a shared external drive connected via usb to an iMac

in the network.

I can see the harddrive over the network but if i want to access it i get

a "operation can't be completed because the original item for "ext hd" can't be found"

If i share a folder on the Mac itself I can access it from another mac and PC over the

network but for some reason that same process doesn't work when it's a

external harddrive being shared.

I've noticed that this is a very common problem on mountain lion.

Has anybody found a solution for this?

Thanks in Advance