FileNotFound exception during msi installation with custom parameter

If you happen to experience an error like

"Error 1001. Exception occured while initializing the installation. FileNotFoundException: Could not load file or assembly c:\\windows\system32\files\aa" while adding custom parameter in custom action in MSI installer. This must be because you have not configure properly the custom property.If you should have more than 1 parameter, all must have backslash except for the last one (e.i /targetDir="[TARGETDIR]\" /customConfig="[CUSTOMCONFIG]" )