Hi Joseph and thanks for the reply,
I will deactivate Active D-lighting on my next try...
There was absolutely no logic on the -0.3EV, it was forgotten from a previous shot. Now,  the circle effect is much less visible, although still there on the following shot
Exif:
File Info 1
File:    DSC_5376.NEF
Date Created:    19/8/2011 9:47:06 ìì
Date Modified:    18/8/2011 7:57:04 ìì
File Size:    10,0 MB
Image Size:    L (4288 x 2848)
File Info 2
Date Shot:    18/8/2011 19:57:03.00
World Time:    UTC+2, DST:OFF
Image Quality:    Compressed RAW (12-bit)
Artist:
Copyright:
Image Comment:                                        
Camera Info
Device:    Nikon D90
Lens:    VR 18-200mm F/3,5-5,6G
Focal Length:    200mm
Focus Mode:    AF-A
AF-Area Mode:    Dynamic, 3D/Wide
VR:    ON
AF Fine Tune:
Exposure
Aperture:    F/9
Shutter Speed:    1/200s
Exposure Mode:    Manual
Exposure Comp.:    -0,3EV
Exposure Tuning:
Metering:    Matrix
ISO Sensitivity:    ISO 250
Flash
Flash Sync Mode:     
Flash Mode:     
Flash Exposure Comp.:     
Colored Gel Filter:
Image Settings
White Balance:    Auto, 0, 0
Color Space:    sRGB
High ISO NR:    OFF
Long Exposure NR:    OFF
Active D-Lighting:    Auto
Image Authentication:
Vignette Control:
Auto Distortion Control:
Picture Control
Picture Control:    [VI] VIVID
Base:    [VI] VIVID
Quick Adjust:    +1
Sharpening:    5
Contrast:    Active D-Lighting
Brightness:    Active D-Lighting
Saturation:    +1
Hue:    0
Filter Effects:
Toning:
GPS
Latitude:
Longitude:
Altitude:
Altitude Reference:
Heading:
UTC:
Map Datum: