Problems with a shared mobile broadband connection

Hi all

I'm using an external mobile broadband modem to connect my PCs to internet. I share its connection with an adhoc network in a Windows 7 PC. IP addressing is set to DHCP and all other computers and devices can successfully connect to the adhoc network, and they have access to internet. The problem begins when a guest computer begins to heavily use the internet, like when starts to download a file. I see the "Windows has detected an IP address conflict" error on the host computer, and the mobile broadband connection stops and won't work until I disconnect and reconnect it.

Any ideas about what's happening and how to fix it?

No one encountered the same?
Is there a way to disable the conflict detection?

My guess and it's just a guess, is that the mobile broad band doesn't have sufficient bandwidth to accommodate all devices.