If you are using Windows firewall, then please go to the below option, click on 'Allow an app or feature' and make sure Notezilla is listed (and it is pointing to the right file - Notezilla .exe in program files). Also make sure that the firewall options to allow the app is enabled. If Notezilla is not listed then you will need to add it. Try all option Public, Private etc.
Above change needs to be done on the computer that is not receiving the sticky note.