3D Sketching -Tab won't change plane

I've had this problem in both 2008 and 2009. Normally, whendoing a 3d sketch, you can change the plane you are working on bypressing Tab. However, it is common for this to just stop working.Pressing Tab has no effect, and I am stuck in what ever plane ithappened to be in at the time.

Do others have this? Is there a way to force SW to change to adifferent plane, other than Tab?

Joe DunfeeSolidworksSketching