NotSupportedException : The mapping of interface member is not supported ....

 Assuming that  item.QuotationId is a LINQ-TO-SQL generated dbType-mapping property meanwhile an interface implementation :

interface ICostDriver

{  QuotationId { get;set;}  }

then if I use the code :

  var itemsInDB = from item in db.Items  where item.QuotationId == quotation.QuotationId select item; 

a Linq-SQL exception will throw :

NotSupportedException: "The mapping of interface member ICostDriver.QuotationId is not supported"

however , If I change the "equal  expression" to another  equivalent manner :

  var itemsInDB = from item in itemTable where item.QuotationId.Equals( quotation.QuotationId ) select item;

The wield exception dissoves.

Don't know why.   Check the thread :

Interface member no supported discussion ...