Those internal errors can occur when MWG has a problem processing the response from the server or has encountered an error while processing the file.
The server response itself seems ok, so it's probably the file - in this case a ZIP archive. For an archive it could be the archive handler or one of the AV engines that can cause this error. I've downloaded the file and the error.log contains an entry for this request:
McAfee Gateway Anti-Malware Engine failed to scan 'PatchKeyboard.exe' - error code 28 (0,0,0)
This error is coming from the integraded third party engine in the Gateway Anti-Malware engine. There is not much you can do to avoid this error (except for whitelisting maybe).
When you upgrade to MWG 6.9 you get Avira as an optional third party engine, it's not included in the Gateway Antimalware anymore. The file will then pass with the default scan options.