When entering your serial number in Native Access, you may be prompted with the error, "The Serial Does Not Belong to a Known Product".
Depending on your OS, Mac or Windows, your solution is a little different.
Windows, delete the following files:
"C:Program Files > Common Files > Native Instruments > Service Center > NativeAccess.xml"
"C:Program Files > Common Files > Native Instruments > Service Center > [LIBRARY NAME].xml"
"C:Program Files > Native Instruments > Service Center > NativeAccess.xml"
"C:Program Files > Native Instruments > Service Center > [LIBRARY NAME].xml"
MacOS, delete the following files:
"/Library > Application Support > Native Instruments > Service Center > NativeAccess.xml"
"/Library > Application Support > Native Instruments > Service Center > [LIBRARY NAME].xml"
"/Library > Preferences > com.native-instruments.[LIBRARY NAME].plist"
After having deleted these files, restart Native Access and add the serial again.