Similar problem here: http://forums.amd.com/index.php?showtopic=47430
The max die temperature for the Socket A is 85C so your temperature is ok (just a little on the warm side). Double check that the heatsink is applied correctly and that you didn't use too much thermal paste (if not using AMD stock).
What is the room temperature that the computer is in? If you have a hot room and the airflow is bad in your case then that will result in higher temperatures.
Are you reporting this temperature from the BIOS or another source?