Hello,
First, thanks for your answer. I'm french and it's hard to give particular details in Shakespeare language
So i take a picture of the problem
The right monitor has the windows start bar
The left monitor is extended desk
As you can see there is a gap (i don't know the english word for "decallage") and with 2 screen at exacly the same position, there is a difference, and no discontinuity.
I try :
- to hide windows bar : no difference
- if i set on "same picture on each screen" : it work, no gap

- the 2 screen have exactly the same setting, (it is exactly the same screen, 2 x Dell 2407 WFP 24")
I download the last update : no change the gap still ther
Well thanks fot your help