Error during run OrganizationRequest 'RetrieveAllEntities' - dynamics-crm-2011

Question

I got this error during execute, could anyone give suggestion? Thanks
OrganizationRequest oreq = new OrganizationRequest();
oreq.RequestName = "RetrieveAllEntities";// please google for available Request Names
oreq.Parameters = new ParameterCollection();
oreq.Parameters.Add(new KeyValuePair<string, object>("EntityFilters", EntityFilters.Entity));
oreq.Parameters.Add(new KeyValuePair<string, object>("RetrieveAsIfPublished", false));
OrganizationResponse respo = orgProxy.Execute(oreq);
"The formatter threw an exception while trying to deserialize the message: There was an error while trying to deserialize parameter schemas.microsoft.com/xrm/2011/Contracts/Services:ExecuteResult. The InnerException message was 'Error in line 1 position 727. Element 'schemas.datacontract.org/2004/07/System.Collections.Generic:value' contains data of the 'schemas.microsoft.com/xrm/2011/Metadata:ArrayOfEntityMetadata' data contract. The deserializer has no knowledge of any type that maps to this contract. Add the type corresponding to 'ArrayOfEntityMetadata' to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding it to the list of known types passed to DataContractSerializer.'. Please see InnerException for more details."

Answer 1

Add a reference to Microsoft.Crm.Sdk.Proxy and Microsoft.Xrm.Sdk. Visual Studio may tell you that you need to add an additional couple System.* references - add them.
Use this code:
IOrganizationService service = GetCrmService(connectionString); //This is a helper, just need to setup the service
var request = new Microsoft.Xrm.Sdk.Messages.RetrieveAllEntitiesRequest()
{
EntityFilters = Microsoft.Xrm.Sdk.Metadata.EntityFilters.All,
RetrieveAsIfPublished = false
};
var response = (Microsoft.Xrm.Sdk.Messages.RetrieveAllEntitiesResponse)service.Execute(request);

Answer 2

Get it work finally there is two KnownTypeAttribute need to be added to the proxy class
**[System.Runtime.Serialization.KnownTypeAttribute(typeof(EntityMetadata[]))]**
public partial class OrganizationRequest : object, System.Runtime.Serialization.IExtensibleDataObject
....
**[System.Runtime.Serialization.KnownTypeAttribute(typeof(EntityMetadata[]))]**
public partial class OrganizationResponse : object, System.Runtime.Serialization.IExtensibleDataObject
Thank you for help.