ASP.NET MVC FileContentResult IE 8.0 hangs on load

some of my users have problems trying to load the report, loading just hangs at 0%, restarting IE usually fixes the problem.

Why is this happening?

I am using ASP.NET MVC (v1), my action looks like this

<Authorize()> _
<AcceptVerbs(HttpVerbs.Get)> _
Function RenderReport(ByVal guid As Guid, ByVal anonym As Boolean) As FileContentResult

    ...

    Dim mimeType As String = String.Empty
    Dim renderedBytes() As Byte = EmployeePresentation.Render(guid, mimeType, Server.MapPath("~/Reports/..."), anonym)
    Return File(renderedBytes, mimeType, filename)
End Function

      

        
        
        
      

    

filename is US-ASCII encoded, file size is usually around 300KB, mimeType is app / pdf

TIA