If the web server isn't configured correctly, or the path to the Images directory in the Control Panel is incorrect, the Web Crossing buttons and other images will be replaced by broken graphic symbols in the browser.

Debug this as you would any web server graphic problem. View the page as source, fix up the relative URL for a problem graphic to be a full URL, put that URL in your browser, then figure out why it doesn't work.

This can be frustrating to figure out, but it is not caused by Web Crossing. Look at virtual paths/directories both in your web server and your OS, do not to use absolute paths (as these won't work in a browser IMG SRC), etc.