Updated form 1.4.8 to 1.5.8 using Fantastico. I know you don't like it. It's an easy way for me ....
Automatic installs and upgrades are an easy way to pain and suffering....
Your upgrade looks to be a bit of a mess. There might be files where they don't belong, as evidenced by:
http://www.debeerst.com/index.php?theme=curveThe source of your upgraded page looks like this:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>www.debeerst.com</title>
</head>
<frameset rows='100%, *' frameborder='0' border='0' framespacing='0'>
<frame name='RTKGKGALDLD' src='http://www.mindex.be/astronomy/index.php'></frame>
<noframes>
<body>
<center>
<a href='http://www.mindex.be/astronomy/index.php'>www.debeerst.com</a>
</center>
</body>
</noframes>
</frameset>
</html>
Which, in my opinion, is not how a cpg page should look.....
Start by comparing the files and folders between the two installations. Clean it until the Curve theme works well. Then try logging in.
Remember that you will need to upgrade your theme to cpg 1.5.xx standards to use it.
For all current and future readers:
"Automatic installs and upgrades are an easy way to pain and suffering" Read your document package.