When uploading a video to SNS, it appears to upload completely and then comes up with the error
“Your video could not be processed because there was an error transferring the file. Please contact your administrator.”
I am not quite sure how to debug this.
This error normally indicates that, SnS is unable to transfer the file to the MXE for transcoding.
If it's a new installation, then I would suggest you to verify that the FTP credentials were properly created on MXE. if it was working before, then, there are a couple of bugs (for example, CSCto65995) that can cause the FTP password on MXE to become invalid, so you may be hitting one of them.
I would recommend you to reconfigure the SnS-MXE integration again and see if it helps