I've been running postfix as a personal mail server for several years but today I rebooted my machine to move to latest kernel and postfix will no longer start. In /var/log/mail, I see the following error:

Apr 27 21:52:28 server postfix/postfix-script[5556]: starting the Postfix mail system
Apr 27 21:52:28 server postfix/master[5557]: fatal: open lock file pid/master.pid: unable to set exclusive lock: Resource temporarily unavailable

I have spent a couple of hours searching Google and have tried reverting to the previous kernel, rolling back to the previous version of postfix and running with the default config (master.cf and main.cf) files but I am still having the same problem.

I'm currently running SLED 11 SP2 with kernel 3.0.26-0.7-default and postfix-2.5.13-0.17.4.

Any help will be much appreciated!