This error is known to occur when there is an issue with file access control on your local machine. Typically this happens when the operating system locks the file or blocks access to the file from the browser. Common situations are:
1. In the case of a PST, if the PST file or an email it contains is open in Outlook on the computer.
Resolution: Close Outlook and try again.
2. The file is inside of a zip and is being dragged and dropped into the GoldFynch screen.
Issue: Windows sometimes shows the contents of a zip inside file explorer, but it cannot be drag-and-dropped from within the zip.
Resolution: Extract the file from the zip fully, and then try uploading the extracted file.
3. The file is in an inaccessible location, e.g. a network drive, or a USB stick
Resolution: Copy the file over to the local drive and then try uploading again.