That’s because your custom command is generating an invalid command:
PostCustomCommandPath = “e:\videocaptures\cleaned files\mcebpostprocess.bat”
PostCustomCommandParameters = “%convertedfile%” %sourcefile% “%destinationpath%” 1080 .%convertedext% 0 %airmonth% %airday% %airyear% %season%##
PostCustomCommandHangPeriod = 0
PostCustomCommandCritical = False
PostCustomCommandUISession = False
PostCustomCommandShowWindow = True
PostCustomCommandExitCodeCheck = False
ERROR> 2017-07-28T16:15:09 MCEBuddy.Engine.ConversionJob → Unhanded error during conversion, conversion cancelled
System.ArgumentException: Illegal characters in path.
at System.IO.Path.CheckInvalidPathChars(String path, Boolean checkAdditional)
at System.IO.Path.IsPathRooted(String path)
at MCEBuddy.Transcode.CustomCommand.Run()
at MCEBuddy.Engine.ConversionJob.Convert()
Your custom command is generating invalid path characters for your command batch file.