Hi HomerJ,
I have seen this before and the resolution was to use either the IP address or the fully qualified domain name (FQDN) for the ALM server. Sometimes the IT routing gets changed and the name doesn't propagate correctly. You need to have your system analyzed and compare it to other systems that are working to find out why yours is different (could be anything from old routing table, switch issue, firewall that is involved and blocking, etc). This is where I would start to see if that resolves it. The internet browser can add on some of the domain extensions and that is why it resolves correctly whereas the ALM Explorer doesn't have that capability and it could be something as simple as the FQDN has the .com added that the address you are trying doesn't include it. I would suggest getting your IT department involved to see why you don't have the correct resolution to the server occurring.
Hope this helps get you started,
Dan