Can you show us the BARCODE reader control's code ? The code that you use for getting the Barcode from the bracode reader.

Change event will be fired each time when a change is made in the textbox.
Example: you want to type 123456 in textbox.
When you type 1, Change event will be executed. And you continue typing the second number ie. 2. Again the change event will be fired. Like that.
That's why, your code is not working.