This following wording comes straight from the Autodesk help file. I've decided to blog about it because it's crucial information for network licenses:
Important: Autodesk 2015 products include NLM version 11.12; all network license servers working with 2015 products must also run NLM version 11.12. The 2015 clients cannot get licenses from a server running NLM 11.11 or lower.
Restriction: Do not install NLM on a remote drive. When you install the NLM files, you must provide a path to a local drive. You must specify the drive letter; the universal naming convention (UNC) is not permitted.
NLM must configure the license servers before any products can obtain licenses and start running, but NLM can be installed either before or after the products that will use it.
If an earlier version of NLM is already installed on the server, uninstall that version, and then install the new version into the directory where the old version was located.
After installing NLM, you typically need one or more network license files. If you have a network license serial number, you may be able to generate the license file by following the instructions at http://registeronce.autodesk.com. Otherwise, contact Autodesk.