It's possible a timeout setting is the cause as there are certain scenarios that can cause a timeout after 90secs. To confirm the behavior I would recommend opening up a case in your customer group here in the Jive Community and providing the following information.
1. The username of the user seeing the behavior
2. The name of the file they are attempting to upload
3. The time they see an error
4. A screenshot of the error they are seeing
5. The Microsoft Office logs from their local machine that include the timeperiod they were conducting their testing in ( https://community.jivesoftware.com/docs/DOC-73552#comment-2050081 )