postmaster: address already in use

Hi,

my postmaster suddenly begins to make problems. It was running fine, but
then:

FATAL: StreamServerPort: bind() failed: Address already in use       Is another postmaster already running on that
port?      If not, remove socket node (/tmp/.s.PGSQL.5432) and retry.
 
/sys/svr/pgs/bin/postmaster: cannot create UNIX stream port

There is no other postmaster running and there is no socket node file in
/tmp

Any hints??
Thank you,

Markus