What am I doing wrong?

[FlipsidE]

Shot these at my niece's b-day party this past weekend, and the majority of them came out underexposed. I started using a diffuser and pointed my flash forward about 2/3 of the way through, and it did make a difference. But, still not great. What exactly can I do?

For all shots, camera in P mode, lens: 28-105 f/3.5-4.5, Speedlite 420 either bounced or through a Lumiquest Mini Softbox. Any ideas on how I can improve next time?

As a forewarning, this is going to load about 3MB worth of pictures:
http://www.wesculbertson.com/photos/csbp/album.htm

Thanks

FlipsidE

[tim]

I see what you mean, many are perhaps 1.5 stops underexposed. The photos do have quite a few light colors in them, I wonder the camera trying to make everything 18% grey is telling it to turn the exposure time down.

I looked at the EXIF for a couple of them, were you using exposure compensation at +2? And when you used the flash, did you use FEC? Also, whatever metering mode did you use? I'd probably have tried partial, locking the exposure on the faces.