This issue is not related to tableau.
Its an issue related to share point. Generally this error is caused due to uploading big sized doc.
Please follow these steps so that you wont get that error:https://support.microsoft.com/en-us/kb/925083
The Sharepoint issue is more related to writing large files and server timing out. I can copy large files (80-100Mb) almost in an instant, so I doubt that's the issue.