All of the Autodesk 2010 and 2011 products have a propensity of corrupting the cascadeinfo.cas file. This file is directly related to the obtaining of a license from LMTools. We have found that when Revit can't find a license from the server you need to do the following:
The current workaround it to rename/remove the corrupt CascadeInfo.cas file following these steps.
Return any borrowed licenses
Check in any checked out licenses and exit all Autodesk products
Rename or delete the corrupt CascadeInfo.cas
The CascadeInfo.cas file can be found in the following locations:
C:\Documents and Settings\All Users\Application Data\Autodesk\Adlm
Windows Vista and Windows 7:
Here's the full Autodesk technical document:
One word of caution. This may cause your corresponding AutoCAD product to crash on startup. We are looking into this and I will post when I get an answer for this.