Got to thinking I could have replanted the plant too deep. Was thinking that could cause the stem rot.
Done a search before I went out.

Went out and checked the neck of the plant to see if I replanted it too deep which I did. About one half inch or so.
Checked the other plants I did and they were replanted without potting mix up around the plant neck. Those plants are doing fine so far.
I took a trowel and removed the sick plant from the container and washed of the potting mix from the plants root.
The roots were healthy and no sign of black root.

_______________________
How to Plant Pansies in Containers 

http://www.ehow.com/how_4879742_plant-pansies-containers.html

"Place pansies at the same level they were in the flat or seedling pot, and then firm the soil around the plants."
_______________________________________________

Have some material in the garage for more containers to build 16"x16"x16"deep for the two squash and Siberian pepper.
Will start on that this afternoon.