One of those annoying things I always forget how to setup. If you've rendered out an animation to frames with an alpha channel, like old Targa format, and used a pre-multiplied alpha channel you need to make a change when compositing in Adobe Premiere. Years ago, Premiere could not handle pre-multiplied alpha channels. I did my compositing back then in old school Combustion. Anyone remember that? Loved that program but I guess Autodesk decided they couldn't compete with After Effects after a few years. Anyway, I was putting together some old frame sequences and just couldn't remember how to get Premiere to recognize my pre-multiplied alpha. You know, you get that black halo around your composited sequence. In Premiere, select the clip, then go to the "Clip/Modify/Interpret Footage" option and under "Alpha Channel" choose "Conform" and check the box for Premultiplied Alpha as shown below:
During my search on the topic online I came across this nice post on the subject by Dennis Koeppl. Thanks.