Problem starting postmaster

I have installed 7.2.2 on MacOSX 10.2 using fink. I shutdown the postmaster,
and am now trying to restart it using

/sw/bin/pg_ctl start -D /sw/var/postgresql/data/ -o '-i'

(fink installs in a non standard location and sets up and super user account
called pgsql instead of postgres)

But I get this error

postmaster successfully started
FATAL: could not set group of /tmp/.s.PGSQL.5432: Operation not permitted
/sw/bin/postmaster: cannot create UNIX stream port

I am guessing it is write permissions somewhere but I can't seem to fix it

Any ideas would be greatly appreciated

Thanks

Adam

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