themeconfigurator add new item not working

[spajza.hr]

Hello,

 

I have a problem with adding new banners in themeconfigurator.

 

When I click add item, the tab shows for half a second and then dissapears before I can click anything.

Very weird... I have checked in Chrome and Firefox so far and the result is the same..

 

Please help someone, what can I do to make it work again?

 

Thank you!