Hi Jen,
Make sure that you are installing ProAnimator version 4.5.1 for After Effects CS3. If you are using an older version of ProAnimator such as version 4.0.0, it is not compatible with After Effects CS3. You can still use your ProAnimator 4.0.0 authorization code for ProAnimator version 4.5.1.
To download the newest version, please visit our download page below:
http://www.zaxwerks.com/download/
In terms of your authorization code, if you are copying and pasting the authorization code, make sure that you are not copying extra spaces in the back. If there are extra spaces in the authorization code field, it will say that your authorization code is invalid.
If you are still having any issues with your authorization code, feel free to contact us at (626) 309-9102, and we will be able to look up your authorization code for you.
Best,
Edward