Question: We currently have an application (Windows service) that connects to another of our applications and grabs invoices. In the invoices there is a RTF field for the footer/header fields. When we grab the data the RTF is converted to plain text with the following code:

```
public static string ConvertFromRTFToPlainText(string rtfString)
{
    if (rtfString == null)
        return null; 

    System.Windows.Forms.RichTextBox rtBox = new System.Windows.Forms.RichTextBox();

    if (rtfString.StartsWith("{\\rtf1"))
        rtBox.Rtf = rtfString;
    else
        rtBox.Text = rtfString;

    return rtBox.Text;
}

```

This has worked for the most part but in some cases (one particular client gets it everytime) I get this exception:

```
Exception Message:Error creating window handle.
Stack trace:
at System.Windows.Forms.NativeWindow.CreateHandle(CreateParams cp)
at System.Windows.Forms.Control.CreateHandle()
at System.Windows.Forms.TextBoxBase.CreateHandle()
at System.Windows.Forms.RichTextBox.set_Rtf(String value)
at SmartTrade.Common.API.Tools.RTFHelperUtility.ConvertFromRTFToPlainText(String rtfString)
at SmartTrade.Desktop.Proxy.API.ObjectMapper.InvoiceObjectMapper.CovertToAPIInvoice(Invoice domainInvoice)

```

Any help on why this is happening or how we can work around it would be much appreciated.

**Edit**: Thanks to Jeremy for the explanation, I am after suggestions for RTF conversion alternatives.

Answer: 
TimeSpan.Add() doesn't modify the existing value, but returns a new resultant TimeSpan. So you'll need to change:

```
sr.Elapsed.Add(ts);

```

... so that it actually stores the result somewhere useful.
See <http://msdn.microsoft.com/en-us/library/system.timespan.add.aspx>

Add returns a new TimeSpan object rather than mutating the existing, and since StopWatch.Elapsed is readonly I don't know if you can accomplish what you're trying