[SOLVED] PowerClip. Invalid Object Error Message

When I try to create a PowerClip and follow the instructions

1. Select an object
2. Click Effects > PowerClip > Place inside a container
3. Click the object you want to use as the container

whatever I choose, artictic text or rectangle, I have the error message "The object you have selected is invalid" Would someone please tell me what I have done wrong. Thanks

OS: XP Pro SP2