At least one object must implement IComparable
Implement IComparable for the Types of the objects contained by CustomerConnection and empcon. If they don't have IComparable implemented then there is no way to perform an order by.
I had this problem with my query when I wrote it wrong:
IEnumerable<OrgRelation> relations = from r in tree.OrgRelations
orderby r.ParentUnit, r.ChildUnit
select r;
This was because the Parent and Child Units are both OrgUnit objects the are related to this OrgRelation entity. What I needed was to order not by the object, but by the property of the object on which I really wanted to sort. When I added the ".Name" it worked.
IEnumerable<OrgRelation> relations = from r in tree.OrgRelations
orderby r.ParentUnit.Name, r.ChildUnit.Name
select r;