If you've ever tried to add a motion activated light switch to a fixture with a CFL bulb you might have noticed that it flickers, unless you had the forethought to shell out 4 or 5 times as much for a dimmable CFL.
Typically the issue isn't with the motion detector or the CFL, but with the photoresistor light sensor bundled with the motion detector to keep the light off during the day.
Step 1: What's Being Removed
Here's a close up of the photoresistor from my model. The photoresistor always has to be someplace in the motion detecting window to allow it to receive light. I cut the leads long in case I need to create a short across the photoresistor instead of an open.