Well, first of all, you are not posting 
exactly what the error message says as I'm pretty sure that Zdoom spells "c
haracters" correctly. 

 Seriously, it is important to post exactly what the report says because it may be saying something that is almost unnoticable (like a very minor typo) thay isn't obvious to see.  I know that has been the problem for me when I have seen this error.
I don't remember if this error gets logged to the console but you could try starting zdoom by adding +logfile log.txt to the command line then open the file log.txt that Zdoom creates and copy/paste the message from there.
However, there is one thing that I have spotted.
If you have accurately reported the name of your sprite "MACHBO", it is wrong.  It should be "MACHB0".  ie, the last character should be a zero, not a letter "oh".