postgresql as windows 2000 service problem

Another weird problem with windows 2000:
As administrator I have run
runas /user:.\postgres "pg_ctl start"
it prompts for a password, I type it and the postmaster is starting
to a new cmd window.

As Administrator I type
runas /user:.\postgres "pg_ctl stop"
it prompts for a password, I type and the postmaster stops. Everything Ok.

I try the same things after a few minutes and a windows error message box
appears (during pg_ctl start) saying about illegal operation and terminates
the process. I checked and there is no postmaster.pid lock file in data
folder left out (postmaster doesn't start).

Some times it works sometimes it doesn't

In windows XP it works fine (as far as I know except I have to type
runas /user:server\postrges "pg_ctl start"
runas /user:server\postrges "pgctl stop"