Multiple issues after error message

I would first make sure you have updated your EndNote to the latest version:

For X7 see

https://support.clarivate.com/Endnote/s/article/EndNote-X7-Updates?language=en_US

For X8 see

https://support.clarivate.com/Endnote/s/article/EndNote-X8-Updates?language=en_US

I would then use the following steps to clean up any document corruption:

https://support.clarivate.com/Endnote/s/article/EndNote-Problematic-field-codes-causing-jumping-cursor-the-range-cannot-be-deleted-or-other-problems-while-formatting?language=en_US

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