Estoy invocando una función de Oracle desde una aplicación .NET y siempre obtengo la siguiente excepción: PLS-00306: número incorrecto o tipos de argumentos en la llamada a 'TF_GETNODES'

Aquí está la definición de la función Oracle:

FUNCTION "IMPACTNET"."TF_GETNODES"
(
    DIMENSIONKEY  IN NVARCHAR2,
    PARENTNODE    IN NVARCHAR2,
    PARASTRING    IN NVARCHAR2
) RETURN IMPACTNET.TREE_NODE_TABLE IS

    treeNodes IMPACTNET.TREE_NODE_TABLE;

BEGIN

    treeNodes:=IMPACTNET.TREE_NODE_TABLE();
    for i in 1..2
    loop
    treeNodes.extend;
    treeNodes(i) := IMPACTNET.TREE_NODE(DIMENSIONKEY || i, PARENTNODE || i, 0, 0, PARASTRING || i, 0);
    end loop;

    RETURN treeNodes;

END;

Y aquí está mi código .NET:

var treeNodes = new TreeNodesTable();

using (var connection = CreateConnection())
using (var command = new OracleCommand { Connection = connection, CommandType = CommandType.StoredProcedure, CommandText = "IMPACTNET.TF_GETNODES" })
{
    command.Parameters.Add("DIMENSIONKEY", OracleDbType.NVarchar2, ParameterDirection.Input).Value = "dimension key";
    command.Parameters.Add("PARENTNODE",   OracleDbType.NVarchar2, ParameterDirection.Input).Value = "parent node";
    command.Parameters.Add("PARASTRING",   OracleDbType.NVarchar2, ParameterDirection.Input).Value = "para string";

    var p1 = new OracleParameter
    {
        ParameterName = "treeNodes",
        OracleDbType = OracleDbType.Object,
        UdtTypeName = "IMPACTNET.TREE_NODE_TABLE",
        Direction = ParameterDirection.ReturnValue,
        Value = treeNodes
    };
    command.Parameters.Add(p1);

    connection.Open();
    command.ExecuteNonQuery();

    treeNodes = (TreeNodesTable)p1.Value;
}