I'm going to assume that "singlecobs" returns a single object of some type. A GridView is designed to show a collection of objects of a given type, not a single object. The error is complaining that it can't treat the datasource you are giving it as a collection.
If you want the grid to show a single object\row you need to make a collection that contains your single object. There are various ways to do this, but the below makes an array that contains your object.
GridView1.DataSource = new YourType[] { dbentities.singlecobs("2") };
Replace "YourType" with whatever type is returned by "singlecobs".