First common question:
Did you zip your directory (your zip file contains one item, the directory), or the contents of the directory (your zip file contains a source directory, an images directory?, and a file named manifest). If you did the former like I first did and several others from what I have seen, you'll see problems like this.
The latter is the way you want to do it, and your zip file should look something like
source <dir>
images <dir>
manifest <file>
And your manifest file should look something like
title=Whatever
subtitle=Whatever whatever does
major_version=1
minor_version=123
build_version=4567
mm_icon_focus_hd=pkg:/images/RokuChannelArt_290x218.png
mm_icon_side_hd=pkg:/images/RokuChannelArt_290x218.png
mm_icon_focus_sd=pkg:/images/RokuChannelArt_214x144.png
mm_icon_side_sd=pkg:/images/RokuChannelArt_214x144.png
hidden=0
splash_screen_sd=pkg:/images/LoadScreen480.jpg
splash_screen_hd=pkg:/images/LoadScreen720.jpg
splash_color=#123456
splash_min_time=0
Hopefully this helps get you started...