[Xymon] RRD Graph stopped graphing

I had two custom RRD graphs setup and running fine on client systems.
The script that collects the data was running every minute. After I finished testing, I changed the frequency of the scripts on the clients to 1 hour in the clientlaunch.cfg file. When I did, the RRD graph stopped displaying data. It ran like this for a couple days. I changed clientlaunch.cfg back to 1 minute... and the graphs immediately started graphing again. Is there a minimum time frame that is needed, or something else that must be done? What am I missing?

-- Michael Beatty