Problem using CLR External Environment in SQL Anywhere 11

I am trying to execute a C# function in an assembly from a stored procedure in SQL Anywhere 11.

C# Code:

using System;
using System.Collections.Generic;
using System.Text;

namespace clrTest
{
    class StaticTest
    {
        private static int val = 0;


        public static int GetValue()
        {
            val += 1;
            return val;
        }
    }


SQL code:

CREATE FUNCTION stc_get_value()
RETURNS INT
EXTERNAL NAME 'clrtest.dll::statictest.GetValue() int'
LANGUAGE CLR;


SELECT stc_get_value();

The output from running the last statement should be 1, 2, 3, 4 by executing the select statement 4 times.

The problem, I get a (NULL) back all the time.

I know the assembly is being found and loaded by SQLAnywhere, because when I unload the assembly, i get an error as :

Procedure 'stc_get_value' terminated with unhandled exception 'Object
reference not set to an instance of an object.'
SQLCODE=-91, ODBC 3 State="HY000".