You might be having a conflict with another addin:
Please see:
https://support.clarivate.com/Endnote/s/article/EndNote-Cannot-edit-Range?language=en_US
If the steps from our website do 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