Retrieve an email template return nothing

I am trying to obtain an email template to modify its content locally, however I can not retrieve by using its api call. I am making the call like this xml-rpc - Keap Developer Portal. In your documentation you do not specify the type of answer. Could you tell me the type of that answer?
I am trying to use it in a CSharp app I receive this error:
An unhandled exception of type ‘CookComputing.XmlRpc.XmlRpcTypeMismatchException’ occurred in CookComputing.XmlRpcV2.dll
Additional information: response contains struct value with missing non-optional members: PieceTitle Categories FromAddress ToAddress CcAddress BccAddress Subject TextBody HTMLBody ContentType MergeContext [response : struct mapped to type EmailTemplateMike]

Thanks for your help.