Launchctl - have never got it to work

Question

I'm looking for some help in getting the lauchctl service to work. I have some python products that work fine when I run them from a command line, but never using the launchctl service. I can load then and I see they are loaded. I can unload them. But I can never get them to 'run'. PS simply shows a status of Ss for the launchctl, then it disappears. There is nothing in the system.log.
Not sure where to start.

Answer 1

I guess I was asking a 'general' question, like has anyone found the service frustrating to debug when it does not work. For example:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>org.jabber.pymsnt</string>
<key>OnDemand</key>
<false/>
<key>Program</key>
<string>/usr/bin/python</string>
<key>ProgramArguments</key>
<array>
<string>/var/jabber/modules/pymsnt/PyMSNt.py</string>
</array>
<key>StandardErrorPath</key>
<string>/var/jabber/modules/pyMSNt/error.log</string>
<key>UserName</key>
<string>root</string>
</dict>
</plist>
The above fails, trying to find out why seems 'hit and miss'. I do know from experience that if I write it below this, it works. In many cases there is either no messages in the log file or you get the spawning error messages.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>org.jabber.pymsnt</string>
<key>OnDemand</key>
<false/>
<key>ProgramArguments</key>
<array>
<string>/usr/bin/python</string>
<string>/var/jabber/modules/pymsnt/PyMSNt.py</string>
</array>
<key>StandardErrorPath</key>
<string>/var/jabber/modules/pyMSNt/error.log</string>
<key>UserName</key>
<string>root</string>
</dict>
</plist>