When you do ap-mode-switch ftp file ip username password and get "Upgrade failed by version mismatched":
Note that file must be a filename and it fails if it is a path like "/tmp/MODEL-VERSION.bin".
From an FTP viewpoint it shouldn't matter whether you specify a path or file, but it seems that the filename contains information if it is applicable to your device. Any path prefix will make this check fail and results in this version mismatch error.
