We are on version 4.0.268.
After saving a knowledge base article, we attempted to add some attachments to it using the + sign. When we click the + sign, we are presented a "Choose file to Upload" window. After selecting the file to be uploaded, we clicked the Open button and an error popup window appears (Note: Outlook Pro 2016 is the name of the file to be attached)

The path is correct, otherwise we would not have been able to browse to the file.
How can we fix this issue?