One of our users is unable to upload a Word document to a folder in the 'Files' tab.
She is able to click upload > select the document > Open
When she clicks Open she then sees an error message (small purple banner) at the bottom of the screen. The banner contains the file name repeated twice with a red exclamation mark in a circle. When she tries to click on the error message it disappears with no pop up window explaining the error.
Other users are able to upload to this folder, they are even able to upload that exact document.