Other topics about Setting Control Functions
The license key are kept in a text file (.lic) located at Factory(E:)\LICENSE\. The E4991B refers to the license codes in all of .lic files under the directory.
If there is no license code, an error occurs and the E4991B measurement application exits.
When you change the storage, copy the .lic files as back up. You can re-create the license number at http://keysight.com/find/softwarelicense with your software entitlement certificate if the option is added with the upgrade kit.