I installed this extension successfully and can't reproduce you problem. Please generate log file to help troubleshooting.
1. Open Finder.
2. Navigate to "Applications/Utilities".
3. Double click "Terminal.app" to launch it.
4. In the Terminal window, input the following command (including double quotation mark) then press "return" key.
cd "/Applications/Adobe Extension Manager CS6/Adobe Extension Manager CS6.app/Contents/MacOS"
5. Input the following command then press "return" key.
sudo touch ExManLog.YES
6. When being prompted, input the password of administrator user then press "return" key. A file named "ExManLog.YES" should have been created in this folder.
7. Try to install extension.
8. After installation failure, exit Extension Manager.
9. Get log files from "/Users/<UserName>/Library/Application Support/Adobe/Extension Manager CS6/". Note that the folder "/Users/<UserName>/Library/" is hidden by default. You can open Finder, press "option" key when click menu item "Go"->"Library" to go into this folder.
10. Send the log files to email@example.com.