Dispose worked for me too - was getting a memory leak / runaway page script until I added the code below to my custom web spell checker dialog's code-behind.  Thanks for the tip FranklinGray.

        protected void Page_Load(object sender, EventArgs e)
        {
           ...

            this.Unload += new EventHandler(CustomSpellCheckDialog_Unload);
        }

        void CustomSpellCheckDialog_Unload(object sender, EventArgs e)
        {
            WSCSpellCheckerDialog.Dispose();
        }

Which version are you using? They fixed the issue for me with the any release after 2007 Vol v2.

Dispose works most of the time, but not all the time.  I have 130+ users, but at least one a day has to re-boot the app due to a memory leak due to the spell checker.  Maybe it has something to do with them remote logging into a server to run the app, don't know, but I do know that it is the spell checker but that's all is on that form that is causing the leak...that and a textbox.  I dispose of it in the FormClosing event like below.

    Private Sub AccountNote_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        UltraSpellChecker1.Dispose()
    End Sub

Thanks for the tip Torrey, but it doesn't help with my issue. It appears WinSpellChecker is loading an instance of the dictionary every time a form is loaded but never gets released when the form is closed.

I've attached a sample program that highlights the issue.