Make sure that you and your admins have the permission flag "ulx seeasay"
If you are a superadmin, you can try this from your server console.
ulx groupallow <group> "ulx seeasay"
ex: ulx groupallow admin "ulx seeasay"
I think it should be noted that the permission to USE asay and the permission to SEE asay are different.
Anyone you want to be able to send messages to admins using @message you would want to give permission to USE asay.
ulx groupallow <group> "ulx asay"
But if you want a group or person to be able to see those messages, you need to allow them to see it using the permissions I outlined above.