If you cannot communicate with the license manager (i.e. you receive an error or the license finder dialog when launching the program), but the license manager shows licenses are available there are a few common things that will cause this to happen.
1) In the programs folder (where the .exe is you run to open the program) there is a licpath.lic file. It could have an incorrect server name. Open it in notepad to verify it has the right server name in it.
2) Incorrect information in the registry. This one is not for the faint of heart. In the Registry editor expand out hklm->software->flexlm license manager and double click the ADSKFLEX_LICENSE_FILE key. If the value is incorrect then this can also cause this issue. It should be "@servername" where "servername"= the name of the server that is running the license manager.
Warning! Problems caused by improperly editing the Windows registry could render your computer/operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft Knowledge Base.
Use the Microsoft® Registry Editor only at your own risk and only after backing up the registry as well as the system.dat and user.dat files as outlined for your operating system in the Microsoft Knowledge Base and in the related Autodesk solution, http://usa.autodesk.com/getdoc/id=TS66513. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.
3) Incorrect information in the Windows Environment variable for ADSKFLEX_LICENSE_FILE in the System variables. It should also be formatted like the registry. @servername
4) This is the new one with 2010 and 2011. There is a file (hidden deep down in the system) that is called CascadeInfo.cas. This file can become corrupted. To replace it, rename the file and launch the program again, it will ask the license manager for a new one and will be created on the fly. On an XP machine look under C:\Documents & Settings\All Users\Autodesk\ADLM.
Warning: Do not delete or rename or open the ProductInformation.pit file.
Those are the four main causes for this issue, however, I've seen others but they're rare.