Please check your preferences in EndNote for the Styles Folder. In EndNote go to Edit > Preferences > Folder Locations On Windows for MAC In EndNote go to EndNote menu > Preferences > Folder Locations.
Double check that it is pointing to your Documents folder and not to some other location.
To reset the folder locations click on the “EndNote Defaults” button.
Once you change the location or reset the default then try editing a style again.
If this does not resolve the issue then:
Please contact Technical Support directly
1-800-336-4474 option 4 then 1
or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US