Maggie -
I think that Jim and Pam may both be partly right.
The questions I have are:
1) How cold is the room you're working in?
2) What are the pans made of?
3) How big are the pans?
4) Are the nuts at room temperature (or colder)?
It's easy to over-temper in a Chocovision machine, just as it's easy to under-temper. A machine like that is no replacement for actually knowing how to hand-temper and how to tell if your chocolate is in temper. The default temperatures may not be the best ones for your chocolate.
If the room is cold and you're using stainless steel bowls and they are big bowls and you're dumping cold nuts into the chocolate -- well that would cause it to set up very quickly - especially if you are setting the bowls down on a stainless steel or marble table. Just suck the heat right out of it!
The bowls should be at the same temperature as the chocolate in the temperer, or as close to it as you can manage. You can use a heating pad under a marble slab (or between two sheet pans - this is best!) to create a warm surface to work on.
The nuts should also be as close to the temperature of the chocolate as possible. If you have a small bread proofer that would work, as would an incubator or an oven with just the light on. I would be careful about microwaving as the heating could be uneven and you don't want fat to migrate to the surface of the nuts.
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clay - http://www.thechocolatelife.com/clay/