Planet WRT-414, MAC Address, Clone!?

Hi,

I have Planet WRT-414 Broadband router. He have 4 LAN ports and he is
connected wirelessly to ISP. One computer works fine but more don't.

ISP see MAC address of my LAN network adapters. My user name is in
releation
with only one MAC address. Button "Clone MAC address" did't work.

e.g.
One computer have Internet and then I connect second computer
with same MAC address. Then second computer have Internet but first don't
.

Newly firmware don't exist.


How to get Internet connection to both computers???