We have a single on-premise installation which is giving us a Http 504: Bad Gateway error message in the browser console when I attempt to use the AsyncUpload control. We are using this in a web farm, the web.config file contains the same values in each of the web servers in the farm:
All other installations are fine, but this is not. The temporary upload path shows that the file is uploaded with the ".tmp" extension for every attempt, the upload control shows the file is uploaded and the "remove" button is visible, but the page does not interact with the uploaded file.
Can anyone help us understand why this is occurring? Any ideas where to check next? Thanks.