Static method works on one project but not the other?

Question

I created a project "Control Panel" and I referenced another project called wServer and made a static method in ChatManager class in the wServer project

public static void ControlPanelSay(string text)
        {
            foreach (var i in manager.Clients.Values)
                i.SendPacket(new TextPacket
                {
                    BubbleTime = 0,
                    Stars = -1,
                    Name = "Admin",
                    Text = text
                });
            log.InfoFormat("<Admin>: {0}", text);
        }

When I run this method from wServer project it works fine how it should, but when I run it from the Control Panel project it throws this error:

The code that executes the method:

private void sendChatButton_Click(object sender, EventArgs e)
{
    ChatManager.ControlPanelSay(chatSendTextBox.Text);
}