Sometimes only one GPU is detected when there are two installed.
Or 2 are detected when only 1 is installed, sometimes even an NVIDIA GPU is detected.
First try rebooting your system.
If this fails, you can try removing all drivers and install them again.
This may sometimes solve the problem:
In this folder: C:\Program Files\eFMer\TThrottle\examples you find: tthrottle.xml
Copy tthrottle.xml, it to a temporary folder.
Change:
<!--
<GPU_SETUP>
<ati_number_gpu>1</ati_number_gpu>
<GPU_SETUP>
-->
Into
<GPU_SETUP>
<ati_number_gpu>2</ati_number_gpu>
<GPU_SETUP>
The digit is the number of GPU's you have actually installed.
Save the edited tthrottle.xml and copy it to C:\Program Files\eFMer\TThrottle
Exit TThrottle and restart TThrottle.