Unable to create scaled Thumbnail image

Whatever I do i still get the message :

ngm1999_04p112-3
* View
* Edit
* ngm1999_04p112-3's thumbnail derivative image was missing. The derivatives will be rebuilt to regenerate it.
* ngm1999_04p112-3's preview derivative image was missing. The derivatives will be rebuilt to regenerate it.
* The derivative images for ngm1999_04p112-3 have been regenerated.

Unable to create scaled Thumbnail image

Some information about my system:

PHP Version 5.2.6
Drupal 6.6

Status report
GD library Not installed
The GD library for PHP is missing or outdated. Please check the PHP image documentation for information on how to correct this.

Therefore added into phpini:

extension=php_gd2.dll
extension_dir = "D:\PHP\ext\"
File is also located there

Then : no GD section is displayed via phpinfo().

No other errors can be found or log files.

Then installed ImageMagick. But can't set that a a primary image toolkit ... strange...

What is wrong here? Did I something strange? What other info is needed to understand this problem?