Using `InsertFile` and saving the file from website on IIS

I am trying to add a file on a word document

application.Selection.InsertFile(file);

But it causes the exception

COMException: The document name or path is not valid

And then save it

document.SaveAs(path);

But then I get the exception

The object invoked has disconnected from its clients. (Exception HRESULT: 0x80010108 (RPC_E_DISCONNECTED))

The exact same code works when running from Visual Studio. The exception only happens when I try to run from IIS.

Could it be related to some permission? I have given full control permissions to Everyone, ISUSR, Network, Network Service, System, Administrators... And I also tried to use Impersonate with an administrator account.

How can I fix it so it will work when I run from IIS?

Here is the class I made to manipulate the doc: http://pastebin.com/yB2s0jn4

And here is how I am calling it

using (var doc = new HtmlWordDocument(outFile))
{
    // calls Selection.InsertFile( file )
    doc.WriteContent(tempFile);

    // calls document.SaveAs()
    doc.Save();
}

Have you tried impersonation (How to implement impersonation in an ASP.NET application)? like below:

System.Security.Principal.WindowsImpersonationContext impersonationContext;
impersonationContext = 
    ((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();

    using (var doc = new HtmlWordDocument(outFile))
    {
        // calls Selection.InsertFile( file )
        doc.WriteContent(tempFile);

        // calls document.SaveAs()
        doc.Save();
    }

impersonationContext.Undo();