account update error through crm sdk?

Hello - I'm trying to make an Account update through the SDK using the Organization.svc. Here are a few lines of key code:

entity = serviceProxy.Retrieve("account", accountId, columnSet); entity["ownerid"] = new EntityReference("ownerid", new Guid("A8AA28B4-9015-DF11-8062-000E0CA08051")); serviceProxy.Update(entity);

I can retrieve the account without issue. However, I need to update the OwnerId which I'm attempting to do in the code above. The attempted update returns the following error:

"The value of 'new_action' on record of type 'account' is outside the valid range."

What am I missing here?