@melvintcs

Your function is declared to return an object fo type "List<Model.customer>". It currently returns an object of type "Model.customer"

To return a list change the code:

public static List<Model.customer> GetCustomer(string custID)
{
Model.customer cust = Data.DAL.GetCustomer(custID);
cust.companyName = cust.companyName;
//return cust;

//create the list object
List<Model.customer> myList = new List<Model.customer>();

//add the customer object to the list. You can add more if you like.

myList.Add(cust);

//return the list
return myList;
}