printing problem with cups

[Joep L. Blom]

  Now for several  months I'm having a mystery that goes beyond my 
understanding..
I hav cups running and three printers, 2 network and one local 
(connected to the cups server).
I can print on all three so apparently there is nothing wrong. However, 
the mystery is the following:
The cups server (ubuntu 10.04 4-core AMD 4 GB) and another ubuntu system 
(ubuntu 12.04 1-core 64-bit AMD 1 GB) will not print on one printer 
(Brother-mfc-440CN). However, the web-interface to cups 
(http://localhost:631/) gives no error. Every file - even test-pages - 
are presented as printed the only anomaly is that sometimes in the 
error-file the following error is given:
--------------------------------------
E [22/May/2012:12:51:25 +0200] Returning IPP 
client-error-document-format-not-supported for Send-Document 
(ipp://localhost:631/printers/Brother_MFC-440CN-2) from localhost
---------------------------------------
But not always. To add peculiarity to mystery, when I try to print from 
a guest (XP) in VMWare on the system that also runs the cups server, 
that goes without a problem!

When I look in /var/spool/cups/ I see all spool files from the start of 
the problem (and that was already in 2011).
I have tried reinstall of cups but nothing helps.
The only strange thing I see is that the files in the /var/spool/cups 
directory all belong to group lp and that group has no members (the 
owner of the files is root but that is a member of every group).
I would be very grateful for anyone who can shed some light in this mystery,
Joep