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Thread: Error: Unable to cast COM object of type 'System.__ComObject' to interface type..

  1. #1
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    Question Error: Unable to cast COM object of type 'System.__ComObject' to interface type..

    I am working on integrating a NAvis Viewer in my Web Application. I am using the Navis API for listing the clashes in a Dropdown.
    But I get the error:
    Unable to cast COM object of type 'System.__ComObject' to interface type 'NavisWorksAPI6.InwPluginsColl'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{D74F889B-01BA-11D5-A066-00B0D011BBC8}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

    using System;
    using System.Data;
    using System.Configuration;
    using System.Collections;
    using System.Web;
    using System.Web.Security;
    using System.Web.UI;
    using System.Web.UI.WebControls;
    using System.Web.UI.WebControls.WebParts;
    using System.Web.UI.HtmlControls;
    using NavisWorksAPI6;
    using NavisWorks6;
    public partial class Clash : System.Web.UI.Page
        nwOpState m_state;
        InwOpClashElement m_clash = null;
        DocumentClass m_doc;
        public const string NWD_FILENAME = "C:\\Program Files\\Autodesk\\Navisworks Manage 2009\\API\\COM\\examples\\clashtest.nwd";
        protected void Page_Load(object sender, EventArgs e)
        protected void Button1_Click(object sender, EventArgs e)
            m_doc = new DocumentClass();
            m_doc.Visible = true;
            m_state =(nwOpState)m_doc.State();
            m_state.CurrentView.ViewPoint.Paradigm = nwEParadigm.eParadigm_APPLICATION;
            foreach (InwPluginsColl plugin in (InwPluginsColl)m_state.Plugins())  // ERROR LINE
                InwPlugin plugin1;
                plugin1 = (InwPlugin)plugin;
                if (plugin1.ObjectName == "nwOpClashElement")
                    m_clash = (InwOpClashElement)plugin;
            if (m_clash == null)
                Response.Write("Failed to find clash detective");
            foreach (InwOclClashTest clashTest in m_clash.Tests())
                ListBox1.Items.Add("# CLASH TEST - " + + "#");
                ListBox1.Items.Add("New Result:" + clashTest.NumNewResults);
                foreach (InwOclTestResult clashResult in clashTest.results())
                    ListBox1.Items.Add("- RESULT[" + + "] Status[" + clashResult.status + "]");
        catch (Exception ex)

  2. #2
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    Default Re: Error: Unable to cast COM object of type 'System.__ComObject' to interface type..

    I had the same problem so i guess it is a bug of Navis. I got over it using late binding, when there's no need to cast.

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