Airprint via CUPS and Avahi doesn't work

Airprint via CUPS and Avahi doesn't work

I installed CUPS and Avahi Daemon as it is documented here on a debian
squeeze.
I can see the printer with my iPhone with iOS 6.1.3, so i guess avahi
works fine. I can print a test page via the CUPS webinterface, so the
printer itself and CUPS are working fine too.
But if i send a printing job to the airprinter with my iphone nothing is
printed. I can't even see a job in the CUPS webinterface. It worked once a
while ago when i first tested the setup. But just a view days later when i
tried again nothing happened...
How can I debug where the job is lost?
My services file
/etc/avahi/services/AirPrint-Brother_HP_LaserJet_4050_Series.service looks
like
<?xml version="1.0" ?><!DOCTYPE service-group SYSTEM
'avahi-service.dtd'><service-group><name replace-wildcards="yes">AirPrint
Brother_HP_LaserJet_4050_Series @
%h</name><service><type>_ipp._tcp</type><subtype>_universal._sub._ipp._tcp</subtype><port>631</port><txt-record>txtvers=1</txt-record><txt-record>qtotal=1</txt-record><txt-record>Transparent=T</txt-record><txt-record>URF=none</txt-record><txt-record>rp=printers/Brother_HP_LaserJet_4050_Series</txt-record><txt-record>note=Brother
HP LaserJet 4050 Series</txt-record><txt-record>product=(GPL
Ghostscript)</txt-record><txt-record>printer-state=3</txt-record><txt-record>printer-type=0x1014</txt-record><txt-record>pdl=application/octet-stream,application/pdf,application/postscript,application/vnd.cups-raster,image/gif,image/jpeg,image/png,image/tiff,image/urf,text/html,text/plain,application/openofficeps,application/vnd.cups-banner,application/vnd.cups-pdf</txt-record></service></service-group>