Trial and Error rules
With no programming skills I compied component.php from another template, pasted it, adjusted it, and low and behold .... Now everything works perfectly.
[code:1]<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="
www.w3.org/1999/xhtml" xml:lang="language; ?>" lang="language; ?>" dir="direction; ?>">
<head>
<jdoc:include type="head" />
<link rel="stylesheet" href="<?php echo $this->baseurl ?>/templates/coolness/css/template_css.css" type="text/css" />
</head>
<body class="contentpane">
<jdoc:include type="message" />
<jdoc:include type="component" />
</body>
</html>[/code:1]
Maybe you ought to include such a component.php in your template package - I don't know, but it might be needed for some other things as well....