使用XML数据类型调用存储过程

I am simply trying to call a store procedure (SQL Server 2008) using C# and passing XMLDocument to a store procedure parameter that takes a SqlDbType.Xml data type. I am getting error: Failed to convert parameter value from a XmlDocument to a String. Below is code sample. How do you pass an XML Document to a store procedure that is expecting an XML datatype? Thanks.I am simply trying to call a store procedure (S