Sorry, I don't understand what you want to do.
Render a still?
Maybe you're trying to define the thumbnail image of a rendered clip? (After Effects can't do that.)
Hello Andrew, sorry about my english :-)
Yes I'm trying to define a special thumbnail image of a rendered clip from my timeline - I can't believe it, that AE CS6 this not can??? In a little clip with 15 sec it will rendered any picture in the middle of the timeline...I can't believe it !!! THE GREAT PROGRAMM AE CS6... :-(
You are really sure?