vncserver interferes with local xfree users

[scoazera]

When "vncserver" starts (on screen :29) while a local user
is working on "xorg" (kde, wmaker...), the local user will not be able
to run any graphic application.
The strange error is:
Error: Can't open display: 0.0

After the local user logs out and logs in again, local "xorg"
works again properly.

But if "vncserver" dies and I have to start it again,
the problem raises again.