Reddish Tint?

Just did a shoot for a local restaurant, using 30d, 17-40L and 430ex. Not all but a good 40% of the images have a red tint to them.

What went wrong?

Thanks

How about posting one of them?

need to see the evidence and the settings of the camera before the problem can be examined.

What was the lighting like in the restaurant? Did you shoot RAW or JPEG, what did you set the white balance to?

Posting sample would help.
It's likely a simple White Balance error from mixed commercial lighting combined with flash.

WB choice is made by the camera sensor interpreting:
Color Temp, which is blue-yellow/amber color axis, and
Tone, which is green-red/magenta color axis.

In mixed commercial light + flash my experience is 30D interprets WB wrong about 80%+ of the time. My 1-DMkII gets WB correct more in mixed light.
This is just a fact. Film had the similar problem. Digital is easier.

1. This fact made me religious Whi-Bal user (I own three).
2. This fact made me shoot RAW, with fast NONDESTRUCTIVE Batch "Click-WB" correction. WB is among things you can fix nondestructively in RAW.
3. You can shoot at 1/200 or 1/250, adding more background flash, to eliminate ambient light from the shot.
4. Sometimes mixed commercial lighting is so ugly, get them to turn it off and bring more flash, or use it to creative advantage as long as no skin is in the shot.
Jack

usually, AWB or even Tungsten WB is poor with dslr's. I suspect that's the cause, if you shot in RAW, you can correct it easily.

I never trust AWB. More on that here: Gray card: Why your meter may be lying to you!
Notice that the very last exposure in the 2nd group was of a gray card.