UserControl Design Mode when Lib ois Imported

Question

    public partial class StartUPEmbedded : UserControl, IMessageFilter
    {
        public StartUPEmbedded()
        {
            InitializeComponent();
            if (this.DesignMode) return;
            this.ParentForm.FormClosing += new FormClosingEventHandler(StartUP_FormClosing);
            con = new Conversation("itbrigada");
            con.Hide();
            Broadcaster.Connected += Broadcaster_Connected;
            client = new CommunicatorClient();
            client.Responder = new Broadcaster.DResponder(Responder);
            client.Start();
            Application.AddMessageFilter(this);
            MailBox.MailBoxUpdate += MailBox_MailBoxUpdate;
        }

just th epart of the UserCitrl that has done in different solution.. same .NET.. imported Ok.. but..

when drag and drop it on the form I get the error message: says nullreference at line and it corresponds to the next after

if(this.DesignMode) return;

What's wrong? Any other condition? Tried to place all that below lines inside OnLoad - then was able to drop, but it was frozen and even the DevEnv reloaded the whole solution.. ??? ))

this.DesignMode doesn't work in that case?