3ds Max - Error 20

3ds Max (Win7) - The Software License Checkout Failed. Error 20

Delete 'C:\ProgramData\FLEXnet\adskflex_00691b00_tsf.data'

Delete 'C:\ProgramData\FLEXnet\adskflex_00691b00_tsf.data_backup.001'

When you restart 3ds Max, the files will be regenerated and activation is possible again.

(If removing the files is impossible, open 'Windows Task Manager' and close any Autodesk affiliated programs. You will see Autodesk by description of the programs in Task Manager. Also 'LMU.exe'!)