I don't think that'll work. It shouldn't matter, and I'm not sure if ' is valid for xml.
This code should work, I can't exactly test it as I dont' have plus at the moment but I'm 99% sure its valid.
code:
function OnGetScriptMenu(Location)
{
var ScriptMenu = "<ScriptMenu>";
ScriptMenu += "<MenuEntry Id=\"MnuAbout\">About...</MenuEntry>";
ScriptMenu += "</ScriptMenu>";
return ScriptMenu;
}
function OnEvent_MenuClicked(MenuItemId, Location, OriginWnd)
{
if(MenuItemId == "MnuAbout")
MsgPlus.CreateWnd('Window.xml', 'About');
}