What's Going On In This Picture
 

This picture was taken in RAW and then converted but in all formats lines are visible in the background. They seem most visible in the right upper corner. Can anyone tell me what is causing them?

Its vertical banding, what ISO was this taken at?

It was taken at ISO 100. Here's the complete EXIF.
File name
IMG_9268.CR2
Camera Model Name
Canon EOS 20D
Shooting Date/Time
2/4/2007 15:12:17
Tv(Shutter Speed)
1/400Sec.
Av(Aperture Value)
F13
Metering Modes
Partial metering
Exposure Compensation
0
ISO Speed
100
Lens
75-300mm
Focal Length
270.0 mm
Image size
3504 x 2336
Image Quality
RAW
Flash
Off
White Balance
Auto
AF mode
One-Shot AF
Picture Style
-
Parameters
Tone Curve : -
Sharpness level : -
Pattern Sharpness : -
Contrast : 0
Sharpness : 0
Color saturation : 0
Color tone : 0
Color matrix
-
Color Space
sRGB
File Size
6637 KB
Dust Delete Data
No

Nikon had a small issue with vertical banding with their D200 when first released. It occured at higher ISO's and required the problematic body back to Nikon for adjustment to cure the problem. Only a small percentage of D200's showed this problem and was probably caused by maladjustment on the production line.

I have never known vertical banding on Canon but this is not my area of expertise. I would call your nearest Canon service centre and discuss the problem with them.

This is the first time I've seen this. I'll try a few more shots then if the problem still exists I will follow your advice.