Using multilog with maildrop

Hi,

I've been using multilog with maildrop by including the following in my 
.qmail-default:

| preline -f /usr/bin/maildrop  mailfilter |  multilog s1000000 n20 
/var/log/maildrop

I specify the logfile in my maildropfilter as follows:

logfile "/dev/stdout"

Now, this works OK, until more than one delivery gets attempted at the 
same time and I get the following error from qmail:

2005-07-13 18:27:27.987726500 delivery 2: deferral: 
multilog:_fatal:_unable_to_l
ock_directory_/var/log/maildrop:_temporary_failure/

Can anyone suggest a way round this problem?

R.