The error message you are getting is not referring to the details of the connection, just that the connection file cannot be found.
You should be able to resolve this problem by going into the CSSMenuWriter > cssmw_home > menu.php. In here you can update the include to have an extra ../ in front of it like this:
require_once($WA_dotDotSlash . "../Connections/PowerStoreConnection.php");
This path should be configured for you already though with the code. Do you get this on every page or only when you try to preview certain pages? Please let us know the details about this issue so that we can look into further if necessary.