I'm not familiar with the BCP utility, but what I see happening is the same thing I'm seeing in the code formatting StackOverflow is using. Notice how the slash after PRUEBA is resulting in the following apostrophe not being recognized. I found another problem here where someone was having to get around the BCP utility using the slash as the escape character.
If the slash in the filepath is registering as an escape character, then the following code should work:
SET @PATH_ARC = 'C:\\PRUEBA\\'
SET @BASEDEDATOS = 'DEMO'
SET @LINEAPRODUCTO = 'MEN'
Notice that with the code above, the StackOverflow formatting is reading it correctly too.
Hope this helps!