strange sketch behavior

I'm using sw2006sp5.x on one machine, and since the prior usage a couple
days back, it suddenly refuses to do an extrude. No matter what the sketch
contains, instead of the preview of the extrusion while it waits for input
of the extrude amount, a msg is displayed "This operation requires a fully
defined sketch". An old sldprt loads and looks OK, but extruding any
sketch in a new sldprt is disabled.
I imported an old copy of the settings and it fixed the problem, so I'm
thinking something in the registry corrupted since the last time swx was
used.
Any idea if a legitimate system option could cause this, or would it more
likely be a mystery corruption thing?

thanks,
bill

 

I've seen this when fully defined sketches is checked in the options and I
accidently have a small line or sketch entity drawn by mistake. Select
areas using a window which will not select your good sketch, but will select
areas where small entities could hide. If endpoints are selected and
deleted, the extrusion then previews and works fine.

Keith

PS Ever tried my mirrored assembly trick?