Instead however, some users are seeing either an "-15000" or "-3526" error, where previously AirTunes functioned properly. The latter appears to be connected to firewall settings, and may be fixed by either giving iTunes access permissions, or disabling a firewall entirely. Apple states that the -15000 error may be triggerable by outdated Express firmware (prior to v6.3), but not all users are reporting success after updating. Some suggest unblocking UDP traffic, once again accessed through the Firewall pane.