'Featured image option' doesn't show 'set as featured image'

Hello,
I hope anyone could help me with this ^^

I installed wordpress on my website. (Also imported my old blogger posts) All works fine, except the ‘featured image’ option.

I installed a theme that supports the featured image. The theme is called ‘clear line’. I also tried other themes that should support the ‘featured image’ option, but the option works with none of the themes.

When I click on the ‘featured image’ option, it does show the popup, but doesn’t show the option to click on the ‘set as featured image’ link.
See my screencap. https://i27.photobucket.com/albums/c191/irrimiriam/Screenshot2011-03-26at093241.png
I’ve seen on screencaps of the ‘clear line’ theme, that this option should be visible.
(see their example: https://vatuma.com/wp-content/uploads/2011/02/use_as_featured_image.png )

I’ve read several blogs, fora and other web pages of people with the same kind of problem, but each time their problem is a bit different, and doesn’t offer me a solution. My popup simply doesn’t give me the option to click on the right button.

I removed and re-installed the theme(s) and all the plug-ins. I even downloaded wordpress again and re-uploaded the folder contents, but so far no changes.

Is there an option I didn’t think of?
I really hope you can help me with this problem.
Thanks very much in advance.

Kind Regards,

M.