Installing theme: Invalid Action Specified

[Shex]

Hello there :D
I remembered the Mys Script yesterday and checked to see whether there were updates and tried the newest script (much has changed, wow!)
So, I installed it to a byethost server, edited the htaccess so that I have a "www." at the beginning of every url as I had problems in the acp with this, and now I wanted to install a new theme, but whatever I do, this happens:


Invalid Action Specified

You specified an invalid action that cannot be completed.


I uploaded an edited version of the elements theme into a new folder in the /templates and wrote "templates/folder/template.html" into the second installation field, is that wrong?


And another issue, my ACP has lost it's style somehow, it's only plain text instead of the click-and-show themes, what can that be?


Thanks a lot for any help, and well done, the new script looks awesome!