Set featured image not working (I read other posts)

Hello everyone.

Im using WP 3.5.2 and a theme called aquablock , I got this project and havent done any customisations myself, the problem is that when i try to set the featured image for the slider, after I select the image I need i click “set featured image” and nothing happens, the window closes.

I have tried:

• Disabling and enabling plugins one by one and all at a time.
• Changing to twenty ten(set featured image works in there)
• Check for JS issues
• Different slider plugins
• Read atleast 50 other posts…
• Update WP(The version was 3.x something before)

Is there anything else I can do? What could be the possible file or lines of causing the featurd image not to work(ie causing the conflict)? At the end it makes no sense for me how a theme could interrupt back-end activities… I would simply write other theme but in this case this is not an option.