Having problems compressing web movie, quality doesn't look good, PLZ HELP

Hi guys,
I used to be able to create a sharp/ crisp clean quicktime 7 web streaming movie in compressor 3 with it's default settings but lately it appears to be compressing a very poor quality QT7 web streaming movie. I have not changed any settings as far as I know.
I have always used H.264 800kbps for High Bandwidth and never had any problems with quality or the way it looked.
Can anyone help me out please.
Thanks,

Zia