I've customized the nop cart and added up some classes into the Nop.Common, Nop.DataAccess and Nop.DataAccess.SQLServer.
the problem is with the DBxxxxxProvider class, it is giving me the error 'Object Reference not set to an instance of object' when it goes to Initialize() and check for
if (s_InitializeException != null) { throw s_InitializeException; }