I'm fairly new to AE, and I have had some problems after keying video footage.
I have keyed my footage as prescribed in the adobe tutorial that is available on this site, using Keylight 1.2. This has worked fine removed my blue background and the presenter looks really clean etc.
The problem that I have is that I have noticed once it has been rendered is that I am getting the image turn red a couple of times during the footage just for a split second. It also only changes the area red that I used the pen and rotobezier tool to mark round the image before I keyed it.
I know that the description of what is going wrong for me isn't the best, but if anyone has had anything similar or knows what I'm talking about then I could really so with some help to stop it from happening.
Have you downloaded the Keylight updates from The Foundry wensite? There were a few bugs in the plugin that only got fixed after CS3 was released. You may also wish to pre-compose your masked layer to avoid the flickering. If this changes the result too much (as Keylight will respond to the missing areas that affect its formula), add a blue solid in the pre-comp thast matches the average key color.
Just like you would any other layer with the "move attributes to sub-comp" option. The function is in the menu under Layer --> Pre-Compose (Ctrl+Alt+C). Basically it "flattens" the buffer and forces the plugin to evaluate the pixels differently.