When the plugin is activated, the W3C Markup validation service finds the following errors:
Line 13, Column 28: value of attribute "id" invalid: "2" cannot start a name
<link rel='stylesheet' id='22-css' href='http://sandkasse.ulfsby.no/wordpress/…✉
It is possible that you violated the naming convention for this attribute. For example, id and name attributes must begin with a letter, not a digit.
Line 43, Column 34: required attribute "type" not specified
The attribute given above is required for an element that you've used, but you have omitted it. For instance, in most HTML and XHTML document types the "type" attribute is required on the "script" element and the "alt" attribute is required for the "img" element.