How to stop a delegate to be serialized in WCF?

How to stop a delegate to be serialized in WCF.

My code is like below:

public delegate void ClientCallback(CommonContracts.IEventData a_ErrorData);

I would like to do this because i am getting below error:

There was an error while trying to serialize parameter http://tempuri.org/:GetDriveResult. The InnerException message was 'Type 'System.DelegateSerializationHolder+DelegateEntry' with data contract name 'DelegateSerializationHolder.DelegateEntry:http://schemas.datacontract.org/2004/07/System' is not expected.

Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.

Please see InnerException for more details.

Can any body help me here?