With new release of Autodesk products come new releases of the Network License Manager - FlexLM - LMTools.   Often new license files will work with older versions of the LMTools...but not this time.  We tried a new license file with 2020 products on LMTools Version 11.14 that worked with 2019 products...but it didn't work for the 2020.  We had to install the newer version of LMtools (11.16.2) to get the license file to work.

Here's the link to download a new version of LMTools.