I wrote this over at XDA when I got stuck with the same issue.
This is regards to using SuperOneClick to root your S2 on 2.3.6
OK, after some hacking around, here's the issue
(and a solution):
In short, this root method doesn't work with Android Version 2.3.6. So if you did the OTA (Over The Air) update from ATT which took you from 2.3.4 to 2.3.6 then SuperOneClick Root version 2.3.3 won't work. It will hang on step 5 or 7.
That being said, until there is an updated method to root the Android 2.3.6 version from ATT, you can easily go back to 2.3.4
*then* use SuperOneClick which works.
First, make sure you have *ALL* the drivers. If not, download and install Kies from Samsung, which will install them for you:
Kies
Once you have Kies installed, I followed these steps to get back to 2.3.4:
Download the Odin package with the stock ATT ROM here:
Download GalaxyS2ATT/unroot/ATTGalaxyS2Unroot.zip at DownloadAndroidROM.com
In that ZIP file will be Odin and the stock ATT ROM. Unzip it, and open Odin. Follow the steps in this youtube to put the 2.3.4 ROM back on your phone:
How to Unroot AT&T Galaxy S2! [SGH-i777] - YouTube
Once you're back to 2.3.4, use version 2.3.3 of SuperOneClick to root your phone.
YMMV. I *just* went through this on my SGH-I777 and it works. I'm back to 2.3.4 with root installed.
Cliffnotes:
Install Kies.
Download Odin and ATT stock ROM.
Flash back to Android 2.3.4
SuperOneClick 2.3.3 to root your Android 2.3.4 phone.
*DO NOT* do the OTA upgrade (if ever prompted) as this will unroot your phone.
Mods: Please move or split this reply if needed. I figured I'd post it here as I was stuck where others were and figured it'd be best / most helpful in this topic.
Hopefully this will help some of you that are stuck at step 5 or 7 with Android 2.3.6.