Has anyone had succes in accessing a stored procedure from a SqlDataProvider passing Table-Valued Parameters?

I'm pretty sure it can be done and my problem is between my keyboard and my chair.

I declared a user defined type and stored procedure as such:

CREATE TYPE string_list_tbltype AS TABLE (s varchar(max) NOT NULL )

create procedure dnn_jefftest
    @PortalID int,
    @fromlist string_list_tbltype READONLY,
    @howmany int
as
set rowcount @howmany
select * from dnn_myMessages
where PortalID = @PortalID and MessageSender in (select s from @fromlist)
set rowcount 0
 

Then I have an implementation of:
        public override IDataReader GetMessageList(int PortalID, int HowMany, List<string> FromList)
        {
                return (IDataReader)SqlHelper.ExecuteReader(ConnectionString, GetFullyQualifiedName("jefftest"), PortalID, FromList, HowMany);
        }

SqlHelper throws an execption: Parameter count does not match Parameter Value count

I'm sure that I'm not formulating the parameters correctly, anyone have a suggestion / answer?

I really don't want to use dynamic SQL for this, there are performance & security implications that I'd prefer not to have to deal with.

Thanks!