Under plan9 the user who boots a machine has rights to its filesystem,
so unless you are accessing a remote plan9 file server which is running
an auth server I doubt your problems are to do with administration rights.

Somtimes plan9 will produce slightly misleading error messages, permission
denied might be saying the OS will not allow you to do what you wanted
because it doesn't make sense.

What I suspect is that you didn't chmod your startup (riostart) script
to make it executable?

If this isn't the problem can you cut and paste the exact command that produced
the permission denied error?

I have attached my startup script for interest, it lives in my $home/bin/rc/startup
(other script names are available).

-Steve