postmaster: StreamConnection: accept: No such device or address

Using a legacy installation ( 7.2.3 ).
Occasionally the system will reach a state where attempted psql
connection attempts fail, with the following error in the postgresql
log:
postmaster: StreamConnection: accept: No such device or address

Will also occasionally get "no connection to server" errors from ecpg
programs ( which I believe are probably due to the same issud ).

Can anyone shed some light on what could be causing this?  OS resource
limitation?  Known bug in ancient version of PG?

thanks,
reid