You can first try clearing your browser cache.
You can also try removing any .enw or .ris files from your download folder. If the download folder is full of these types of files that can cause this type of issue.
If the above does not resolve the issue:
Please contact Technical Support directly
1-800-336-4474 option 4 then 1
or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US