PInvoke FatalExecutionEngineError in Diffrent Thread

my code is working fine, but after 5-10 minutes, I get the following error;

Managed Debugging Assistant 'FatalExecutionEngineError' : 'The runtime has encountered a fatal error. The address of the error was at 0x641ad419, on thread 0x5d0c. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.

Called from different threads;

InvokeUtil.getInstance.Calculate(localVal);

My Code;

public class InvokeUntil
{
    private IntPtr m_object = IntPtr.Zero;
    private static InvokeUntil Self;

    private InvokeUntil()
    {
        this.m_object = InvokeUntil.DllCreateInstance();
    }

    [DllImport("xDll")]
    private static extern IntPtr DllCreateInstance();

    [DllImport("xDll")]
    private static extern void DllDisposeInstance(IntPtr CSObject);

    [DllImport("xDll")]
    private static extern void DllCalculate(IntPtr pCSObject, byte[] pCurrentData, uint[] pResult);


    public static InvokeUntil getInstance
    {
        get
        {
            if (InvokeUntil.Self == null)
                InvokeUntil.Self = new InvokeUntil();
            return InvokeUntil.Self;
        }
    }

    public void Calculate(uint[] EffVal)
    {
        InvokeUntil.DllCalculate(m_object, Data.MyData, EffVal);
    }
}