Both of the visual control objects, for upload (AXFFile) and download (AXFFileDownload), are missing documentation for a property called SuppressPopupTransferError. When set to "true" this property should suppress the display of any transfer errors that XFile's visual controls attempt to display. By default, XFile will display these errors even if error handling is in place in the script.

To use this property effectively, use XFile's start method with

On Error Resume Next

and set

[visual control object name].SuppressPopupTransferError = True