well, I tried both solutions (christiant123 & AgamemnonS)
from AgamemnonS:
the file '/var/cache/bind/managed-keys.bind' already existed there, with the right ownership
I then tried your second solution, with the option managed-keys-directory "/etc/bind"; in named.conf.options and by creating an empty "managed-keys.bind" file in /etc/bind with bind as owner of the file, but after that, I couldn't start my bind server anymore.
==> ../bind/bind.log <==
01-Dec-2011 20:35:12.294 general: error: journal.c:171: unexpected error:
01-Dec-2011 20:35:12.294 general: error: missing SOA
from christiant123
I then tried that solution and added include "/etc/bind/bind.keys"; in named.conf.
Same error on restart.
I then changed the ownership of the 'bind.keys' file, who had root ownership, to bind and it worked.
I'm no expert with bind, as I only use it to play on my small home lan network, so I can't say why it wasn't working with the first solution, but anyway, thanks for giving me a solution to this problem.
I'll RTFM for sure one day