WebBrowser document cast not valid

Exception Type: System.InvalidCastException
Message: Specified cast is not valid.
Source: System.Windows.Forms
Stack Trace:
   at System.Windows.Forms.UnsafeNativeMethods.IHTMLDocument2.GetLocation()
   at System.Windows.Forms.WebBrowser.get_Document()
   at InteriorHealth.EmbeddedBrowser.frmMain.CardRead(String strData) in E:DevelopTestProjectfrmMain.cs:line 265
   at MyTest.frmMain.prtCardReader_DataReceived(Object sender, SerialDataReceivedEventArgs e) in E:DevelopTestProjectfrmMain.cs:line 355

this.webKiosk.Document.InvokeScript(ConfigurationState.CardReader.Error.FireJavaScriptMethod);

CardRead(strCardData_m);