This could be well off the mark but is worth mentioning as it is a strong possibility. I found all of a sudden I could not access my website or control panel from my computer, but could elsewhere. Turned out to be the firewall I had running. Check whether these users are running software firewalls. If they are, try access with the firewall disabled. If this works you will simply need to add LP IP address range to the firewall accept list on the computers. Support could probably e-mail the IP range to you.

Hope this helps.  

I think you hit the nail.  I will find out what they are accessing the net with.