If you are able to do it in project manager and if its failing in ZP, then add pauses between steps.
Sometimes ZP does things too fast for the website to complete processing.
Also, which step is it failing on? Check the log in the ZPoster and see which step it is hanging up on, that can give a hint as to what's being caused (in case additional pauses aren't enough to fix it - but that would be my first thought too).