[Exim] local delivery problem

Hi,

I am using 3.12-6 on Debian-i686 woody.

When delivering a mail, the mail remains in the queue and the
following message is stored in /var/spool/exim/msglog:

2000-03-02 15:54:10 sb@??? <root@???>: local_delivery transport deferred: Permission denied: creating lock file hitching post /var/spool/mail/sb.lock.maya.dcs.qmw.ac.uk.38be8ea2.0000222b

What do I need to do in order to have the mail (locally) delivered?

Thank you.

Sergio