Your picking the wrong windows codec. There are two choices: Windows Media Audio v9.1 and Windows Media Audio v9. One is greyed out, one is black. Pick the black one. The greyed-out one is called a smart codec, that when chosen prompts you to install the codec. There is a way to get rid of it, though:
First, make sure dMC is not running in any way, shape or form. By this I mean Audio CD Input, Sveta, dCW, etc.
Go to your dMC Install directory (by default C:\Program Files\Illustrate\dBpowerAMP).
Find the file called "dMCSmartInstall". It is a text file.
Open the file in Notepad.
Delete these three lines:
Code:
.wma
Windows Media Audio
http://www.dbpoweramp.com/codec-central-wma.htm
Reboot your computer and see if you still have two entries for Windows Media Audio.