Problem with Sky Lighting

Does anyone know what causes these lines in the sky? My FS2004 just started doing this, I never noticed it before today. The lines in the sky are worse at dusk. It seems to be related to the lighting. My specs are listed below. I've tried nHancer, no nHancer, every setting in FS2004 but nothing works. I am running FS2004 in 1680X1050. I am using Activesky 6.5 as well. Frame rates are fine (40-60 FPS locked). Any help is appreciated.JimEVGA 790i Ultra MBIntel E8500 overclock to 4.0 GHz/1800 MHz FSB4 GB (2X2 GB) OCZ DDR3 1800 RAMEVGA GTX 260 896MB video card w/latest nVidia driverWindows XP32FS2004 (9.1)