(This is a crosspost from the Autodesk Discussion/forum website that I was participating in)
Since I started here 15 months ago, I've been wary of messing with NLM because I didn't understand it. I still don't know all of it, but I know a lot more thanks to Travis and the rest of the contributors NLM isn't as big of a scary monster as it was before! There were Group Policy entries in my domain that were specifying an environment variable for the local license server (distributed model) by IP address, and then the next biggest office as a secondary, and third biggest as tertiary--by IP address. So for example if you logged in to a computer in site A your environment variable would be ADSK_FLEX_LICENSEemail@example.com;@192.168.2.2;@192.168.3.2 It worked, it was working, so I had no motivation to change it.
While checking some things out on Travis' suggestions, I changed it to a server name, so on my test computer in site C, the environment variable was ADSK_FLEX_LICENSE=@SiteC_server;@SiteA_Server;@SiteB_Server and it worked. I then changed all my environment variables to computer (NetBIOS) names.
That sorted out 4 of my 5 offices, just the 3rd one, Site C users were still grabbing licenses from sites other than their own. Further investigation showed that two of the users who were using the wrong license server hadn't logged out and back in for some time. (this prompted a quick meeting with the CAD Manager and the Sustainability Committee to make changes to inactivity timers and lock computers after one hour, log users off after 2 and go to system standby after 3 hours outside of regular business hours). When one of the problem users logged back in and started up AutoCAD, they did not get a no license error, but rather Autocad seemed to hang for a good 60-90 seconds with an hourglass... after that AutoCAD started up normally and she was on the correct license server. I did the same thing to the the other user and got similar results.
So in the end, there was some sort of networking issue (which is still undiagnosed) that was causing clients to skip over their own license server, but changing environment variables from IP address to NetBIOS names fixed the problem.
Later in 2010 we may implement other changes recommended here and move to a single/redundant license server instead of the distributed model.