To enter the activation key for Notezilla :
1. Right click on Notezilla icon (next to the clock) in the Windows taskbar.
2. Choose Help->Register menu item. The 'Register' window will appear.
3. In the 'Register' window click on the 'Enter activation key' button.
Also, instead of typing the activation key, it would be better to copy paste it.
Make sure that the name specified is same as the license name provided when purchasing the product.