I was trying to draw a MovieClip into a BitmapData object and it just wasn’t working. I turned on warning messages in FlashTracer and saw that there was a Security Violation. It turns out that a streaming FLV that played at the start of my movie wasn’t being removed, and there’s a security feature not to allow a screen grab of a streamed FLV. Once I removed the FLV, parent clip, and closed the NetStream and NetConnection, the grab worked fne. Not sure which part of the tidying up was the fix.