RHN Satellite Server (spacewalk) repomd.xml not found

"repomd.xml not found"
If you add a channel, or if your RHN cache gets corrupted, and one of your guests complains that it cannot find repomd.xml for jb-ews-2-x86_64-server-5-rpm (for example) - you need to rebuild your repodata cache.

Normally this is an automated job - which is exemplified by the fact that you have obviously built out your entire Satellite environment and never had to do any of the steps you are about to do.

So - some prep work:
Open 3 terminals to your Satellite Server and run:

# Term 1
cd /var/cache/rhn
watch "ls -l | wc -l"

# Term 2
pwd
cd /var/log/rhn
tail -f rhn_taskomatic_daemon.log

# Term 3
satellite-sync --channel=jb-ews-2-x86_64-server-5-rpm

Once the satellite-sync has completed, you >should< see the count increment by one.  If you are unlucky (like me) you will not.
You then need to login to the Satellite WebUI as the satellite admin user.
Click on the Admin tab (at the top)
Task Schedules (on the left)
find the Schedule Name "channel-repodata-default" and then click on "channel-repodata-bunch" on the right (under Bunch)
Then click on "Single Run Schedule" and wait about a minute.
Logout of the Satellite WebUI.

If you don't see the ouput in Term 1 increment by 1 at this point, open a case with Red Hat.