That import error is probably due to a non-valid URL for CartoDB, as it needs the URL to give directly a file in a supported format.
What usually happens with Google Drive, Dropbox, Sharepoint and similar services in general is that the URL to share them is not a direct download URL to the exported table but it's an URL that sends you to an HTML site. In these cases, CartoDB downloads this HTML code, which is not a supported format, and the import crashes.
I'm not very familiar with Sharepoint but if the system allows you to get a direct download URL you might want to try that. Platforms like Dropbox usually block those direct links if they see lots of activity for the resource and they add an intermediate step of sending you to an HTML page with a download button instead of giving you the file directly. For this reason, using the Google Drive and the Dropbox connector is the approach to follow to get your files from those services, as URLs might stop working, but unfortunately there's not any Sharepoint importing integration at this moment.
