Under the references for the class library I changed the removed the old version of dll and added the new dll. When ever my business logic library tries to create an object to this library it gives me the following error:
eConnect = new EConnectIntegrationGroup(cnString);
Could not load file or assembly 'Microsoft.Dynamics.GP.eConnect.Serialization, Version=12.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040