What xcal means, I believe, is that some modules in the theme are very old and should really be replaced by modern ones if the theme is to be used. For example, if it uses label or shortcut2, you could replace those modules with xLabel. This is most likely a pretty involved process -- especially if you're new to LS -- so just like xcal I would recommend you to try another theme. Considering the abundance of themes for LS it's not really worth the trouble updating an old and buggy one, at least not until you learn more. You'll save yourself a lot of headaches by getting some other similar theme.