Failed to contact licence server??

I installed Virtualmin on my server. It worked fine until the company that I colo my server with gave me a new range of IP address allocation.

When I logged in the control panel, I received the following warning:

"A problem was detected with your Virtualmin licence : Failed to contact licence server : Failed to lookup IP address for software.virtualmin.com"

I clicked on "Re-check License Status" and received an error message:

"Now re-checking your Virtualmin licence .. .. a problem was detected : Failed to contact licence server : Failed to lookup IP address for software.virtualmin.com"

Can somebody tell me what has happened and how to fix it?

Thanks for your help!