This was an easy one to fix. All you need to do is delete the library file, add a new one and specify the folders that go into the library.
If you are seeing this:
then you should be:
- opening COMPUTER
- scrolling the left hand menu until you can see LIBRARIES
- right clicking on the offending LIBRARY (in this case MUSIC)
- then right clicking on some blank space and selecting NEW > LIBRARY
- name it MUSIC
- then right click on that library and select PROPERTIES
- click the ADD button and set your music folder (like C:\USERS\<your-name>\MUSIC
- select MUSIC from the OPTIMIZE THIS LIBARY FOR drop down and click OK
- Have a nice day!