No errors, the plugin isn't detected, when I go !warn or 'ulx warn' it does nothing!
Does it show as loaded in your server console during server startup?
What does it say in your server console when you run the command, if anything?
What does it say in your client console when you run the command? (command not found?)
My first guess, without seeing answers to those questions, would be that it's not running from your servers addons folder.