Export a QuickTime movie of you finished timeline, as a self-contained movie (File > Export > QuickTime Movie . . ., check Make Movie Self-Contained).
Take that exported movie into Compressor, and choose the YouTube Sharing pre-set. This pre-set is set to the specs YouTube is looking for.
When done, up load your compressed movie to YouTube.
The easiest, best and most reliable way is to export a Quick Time File current settings and bring that into Compressor. Use Compressor's You Tube Sharing preset for the encoding job. Then use the YT uploader.There is also a YouTube template that will take care of the uploading – but not as reliable.)