Well, what does it say? Are any files broken or something?
Reupload any files that came back with FAIL at the begining.
(Moved to 1.4 General Support since that seems to be what you're running.)
Are you sure? I still see  on your website. What did the plugin say? You must download a fresh copy of the files that said FAIL, and upload them to your server (any customizations you may have made to the files will be deleted though).
Don't say anything ç_ç
Uhmmm i think that  was appeared when I activated a plugin but which
Did you install it correctly? Upload the file to /inc/plugins/ and activate it on your Admin CP. Then it would immediately say something. Try it.
Also, which plugins do you have installed?
Uhm!
I confused plugin, I downloaded Diagnostics.
Say that this plugin is not compatible with mybb 1600, I have it and i didn't know it ._.
So you're using MyBB 1.6?