WPF invoke a control

How can I invoke a control with parameters? I've googled this up, but nowhere to find!

invoke ui thread

This is the error i get:

Additional information: Parameter count mismatch.

And this happens when i do a simple check whether the text property of a textbox control is empty or not. This works in WinForms:

if (this.textboxlink.Text == string.Empty)
   SleepThreadThatIsntNavigating(5000);

It jumps from this if the line to the catch block and shows me that message.

This is how i try to invoke the control:

// the delegate:
private delegate void TBXTextChanger(string text);

private void WriteToTextBox(string text)
{
    if (this.textboxlink.Dispatcher.CheckAccess())
    {
        this.textboxlink.Text = text;
    }
    else
    {
        this.textboxlink.Dispatcher.Invoke(
            System.Windows.Threading.DispatcherPriority.Normal,
            new TBXTextChanger(this.WriteToTextBox));
    }
}

What am I doing wrong? And since when do i have to invoke a control when i just want to read its content?