I also have samsung Galaxy SII and i face the Same Problem before some days. But now i am able to get debug the app in My SII.
Please follow the steps and make sure that you follow it completely then only you cna able to get debug in your phone.
First select the Option to Install App from Unknown Sources.
You will find that option in Setting -> Applicatios -> Unknown sources. Select it as yes.
then Select the Option like USB Debugging.
You will find that option in Setting -> Development -> USB debugging. Select it as yes.
Now, Install latest Samsung Kias In your PC. Reboot Your PC, Eclipse and may be Phone also
Now, Try with connecting the Device.
Hope you will get debugging your app in to your phone.
If not then let me know which trouble you get.
Enjoy. :)