Arcane Tower Power Generator "cannot use right now". Bug?

[coo]

I have the item that is supposed to be placed in the Power Generator to get the elevator going, but when I try to place it into the empty slot in the Power Generator combine window, I get the message "Cannot Use Right Now". Can someone please help? Spoiler is welcome, I haven't the patience to figure out what secret corner of the tower I maybe still need to visit or something like that.

[Jehane]

You have to drag it into the empty slot; double-clicking doesn't do the trick.

[coo]

Oh wow, how unintuititve. But thanks, that was it!

[Jehane]

Glad I could help :)