If you check your license agreement (EULA), you'll see that Autodesk does
not support using a PC as a server or host in any way, such as with Windows
Terminal Server, Citrix, or the Guest Account.
Autodesk allows multiple sessions of AutoCAD on one PC, while only using a
single license from the network license server. This is allowed for the
convenience of one user at one PC. Autodesk could easily configure the
license so that multiple sessions would use multiple licenses, but they have
not, trusting that one user uses one PC.
When you turn the PC into a server, and allow multiple users to share that
license, you are violating the license agreement.
There is a trivial workaround: simply install AutoCAD on the workstations
that are trying to use the Guest Account, and share the network license, as
it is designed.
--Cy--
(I don't speak officially for Autodesk)