Help! No matter how I activate plugins including Snapshot it result to 404 error page!

I'm having serious problem on my server and snapshoting cum putting my sport site into coming soon page! I noticed that when i install, activate and set options in plugins then click save it always redirect to 404 page not found page and here is the recent on one after saving easy coming soon plugin:

How can I solve this? This is serious and its eating away my timeline!!