Some Pics Grainy

[Ramones]

I was taking some pictures of a friend skateboarding tonight, I took about 50 shots and a few of them came out grainy. What could cause this?

Bad one:

One grainy/weird lens flare:

Majority of them are like this though:

EDIT: Some Exif data:
# Camera Make = NIKON
# Camera Model = D40
# Software / Firmware Version = Picasa 3.0
# Exposure Time (1 / Shutter Speed) = 10/2000 second ===> 1/200 second ===> 0.005 second
# ISO Speed Ratings = 250
# Lens F-Number / F-Stop = 56/10 ===> ƒ/5.6
# Exif Version = 0210
# Original Date/Time = 2010:02:11 03:09:28
# Metering Mode = pattern / multi-segment (5)
# Flash = Flash fired, auto mode, return light not detected
# Focal Length = 550/10 mm ===> 55 mm
# Image Height = 679 pixels
# Image Width = 1024 pixels

 

[Tulsa]

What camera and Lens? what settings?

 

[Hooker771]

Id say ISO having to be so high in the dark.

 

[dl4449]

ISO 250
d40
???
Troy

 

[FattyMcJ]

Id say ISO having to be so high in the dark.

I don't agree, though, I don't have a guess.

# Camera Make = NIKON
# Camera Model = D40
# Software / Firmware Version = Picasa 3.0
# Exposure Time (1 / Shutter Speed) = 10/2000 second ===> 1/200 second ===> 0.005 second
# ISO Speed Ratings = 250
# Lens F-Number / F-Stop = 56/10 ===> ƒ/5.6
# Exif Version = 0210
# Original Date/Time = 2010:02:11 03:09:28
# Metering Mode = pattern / multi-segment (5)
# Flash = Flash fired, auto mode, return light not detected
# Focal Length = 550/10 mm ===> 55 mm
# Image Height = 679 pixels
# Image Width = 1024 pixels

 

[Ramones]

anyone have any ideas? I know it's not the ISO

 

[gsgary]

Were they underexposed and brightened in post, looks like it to me

 

[PackingMyBags]

Were they underexposed and brightened in post, looks like it to me

Yup

 

[Ramones]

looking back on my camera, that looks right... I didn't do anything to them though... does picasa auto brighten?