Invaild Operation Exception error !..

Question

 
I have this error while i debug.
you can see error in image ..
http://img441.imageshack.us/img441/4139/mt4error.jpg
 
 
while my mouse over private void Log(String pText) its show me (  "GBPUSDig: 2010/06/24 15:03 1.49866 1.49882\0" )
 
Codes here;
 
private void Log(String pText)
{
// textBox1.AppendText(pText + "\r\n"); // does not put cr lf, why?

textBox1.AppendText(pText);
textBox1.AppendText("\r\n");
}
 
Ty So much.