Cannot grant, deny, or revoke permissions to sa, dbo, entity owner, information_schema, sys, or yourself
As per the comments, if you're already the db owner of that database, than you don't need to grant any permission for the db.

Now, in order to find out what specific permissions you have, you can use the following queries:


find permissions on specific db:

USE AdventureWorks2008R2;
SELECT * FROM fn_my_permissions (NULL, 'DATABASE');
GO

find permissions on all the server:

SELECT * FROM fn_my_permissions(NULL, 'SERVER');
GO



See some other info here: Find out SQL Server Logins and associated Server Roles, on MSDN forum.