[Zope] permission denied error accessing files on disk

[Heiko Stoermer]

this might be off-topic, but it may as well be a zope error - I don't
know.

I have a  Samba-share mounted and a Zope External Method which is
supposed to store files on this share.
The zope user has write access to the share, because if I do a "su -
www-data" I can create and delete files there.
Python makes no problems, either. A test script, run with the uid of the
zope user, can also create and delete files there.
Now if I embed this really simple code in my External Method, I get an
"IOError: Permission denied" from Zope:

fh = open('/BETA/test.txt','w')  # BETA is the mounted share
fh.write('Eat this\n')
fh.close

Any ideas? I've really tried everything that came to my mind, but I
require that samba share to be written to (no nfs!)...

Thanks in advance,
Heiko

--
Heiko Stoermer
MIG Augsburg