I am having this issue as well. I have checked permissions and all are as you specified above. I then deactivated other plugins but the same issue persists. I have wordpress 4.1 – I can get to the skins page and the options dialog box appears which allows me to enter changes. When I click save changes it just spins and spins but never saves the changes or gives me an error so I am not sure what is causing the problem. I made sure wp-content/plugins/flagallery-skins is set to 755 and also tried 777 with no luck. I tried this on minima 1.4 and photoblog skins. Is there anything else I should check?