i logout mi pc (to go to eat) and when i come back in my second monitor i found duplicate taskbar (one above other... like this: = )
i have windows vista home premium.

Are you testing on a desktop or a laptop? Are both monitors attached to the same video card or separate video cards? Are both viewing devices monitors, or is one a TV? Are both using the same type of connection (DVI-D, DVI-i, DVI-A, HDMI, VGA) or are they using different types of connections?

My computer goes to sleep plenty of times and I also log out plenty of times and I have never seen this in W7 nor Vista when I first bought it - so my gut feeling is first to checkout your system setup....

in fact im running in a laptop and the other monitor is sharing the same card.
The duplicated bar was on the external monitor and bouth work fine, but the other was duplicated (above eacho ther)
The conecton is standard monitor output)