I decided to install this app on my archerandangler.com forum and I am now having this exact problem. Getting a 503 server error. Continued attempts to access the edit page will eventually gain access but with the problem shown in the pic.
Could it be related to the php version problem indicated here? http://www.dragonbyte-tech.com/f390/cannot-access-edit-settings-18896-post96009/#post96009
BTW - sorry for re-opening this ticket for my other site but because it is the exact same problem I thought it would be ok.