If the path of a(n included) MRPE plugin contained one or more spaces, the plugin name was parsed incorrectly. Quotes were incorrectly required for the whole command line including parameters within quotes, making it impossible to distinguish between a script path containing space(s) and space-separated script parameters. Now the MRPE plugin path must be enclosed in double quotes (") in order to be processed correctly. The same applies for script parameters with whitespace: also they must be separately enclosed in quotes.
[mrpe] include = C:\Temp\my.cfg
check = Dummy "C:\Program Files (x86)\check_mk\mrpe\check_crit.bat" some parameter "with space"