Fix : Unexpected Error when trying to create Document to integrate with Sharepoint

So you have configured Sharepoint with your CE. Set all the entities needed, but when the user tries to upload a document it gets :

You need to make sure that the user has the right privileges. So you need to go to Security-Security Roles. Open the role the user has and check on Core Entities for "Document Location"

Make sure that the Append To is green, and after that, user can store documents.