I got this error when i use Itestsharp?

Protected Sub ImageButton1_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton1.Click
        Dim doc As New Document(iTextSharp.text.PageSize.LETTER, 10, 10, 42, 35)

        Dim writer As PdfWriter = PdfWriter.GetInstance(doc, New FileStream("C:\sample.pdf", FileMode.Create))

        'PdfWriter.GetInstance(doc, New FileStream(Request.PhysicalApplicationPath + "\sample.pdf", FileMode.Create))

        doc.Open()
        Dim table = New PdfPTable(2)

        Dim cell As New PdfPCell

        cell = New PdfPCell(New Phrase("THIS IS CONTACT INFORATION WHICH IS FIELD BY USER"))
        cell.Colspan = 2

        cell.HorizontalAlignment = 1


        table.AddCell(cell)

        table.AddCell("First Name:")

        table.AddCell(txtfname.Text)

        table.AddCell("Last Name: ")
        table.AddCell(txtlname.Text)

        table.AddCell("Address:")
        table.AddCell(txtaddress.Text)

        table.AddCell("Apt#:")
        table.AddCell(txtapt.Text)

        table.AddCell("Postal Code: ")
        table.AddCell(txtpostalcod.Text)

        table.AddCell("City: ")
        table.AddCell(txtcity.Text)

        table.AddCell("*Province:")
        table.AddCell(DropDownList1.Text)

        table.AddCell("Country: ")
        table.AddCell(DropDownList2.Text)

        table.AddCell("Phone: ")
        table.AddCell(txtphone.Text & vbNewLine & s)

        table.AddCell("E-mail Address:")
        table.AddCell(txtemail.Text)

        table.AddCell("Campus of Interest: ")
        table.AddCell(DropDownList3.Text)

        table.AddCell("Program of Interest:")
        table.AddCell(DropDownList4.Text)


        table.AddCell("How did you hear about us?: ")
        table.AddCell(DropDownList5.Text)

        table.AddCell("CONTACT FORM FIELD DATE AND TIME")
        table.AddCell(Date.Now)

        doc.Add(table)

Access to the path 'C:\sample.pdf' is denied. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.UnauthorizedAccessException: Access to the path 'C:\sample.pdf' is denied. 

ASP.NET is not authorized to access the requested resource. Consider granting access rights to the resource to the ASP.NET request identity. ASP.NET has a base process identity (typically {MACHINE}\ASPNET on IIS 5 or Network Service on IIS 6) that is used if the application is not impersonating. If the application is impersonating via <identity impersonate="true" />, the identity will be the anonymous user (typically IUSR_MACHINENAME) or the authenticated request user. 

To grant ASP.NET access to a file, right-click the file in Explorer, choose "Properties" and select the Security tab. Click "Add" to add the appropriate user or group. Highlight the ASP.NET account, and check the boxes for the desired access.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace: 

[UnauthorizedAccessException: Access to the path 'C:\sample.pdf' is denied.]
   System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) +651
   System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy) +1038
   System.IO.FileStream..ctor(String path, FileMode mode) +64
   CONTACT.ImageButton1_Click(Object sender, ImageClickEventArgs e) +81
   System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e) +86
   System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument) +115
   System.Web.UI.WebControls.ImageButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +33
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1746