The ready built version of the Item Selector on SDL Tridion World, will only work on 2011 SP1, not sure if it still works for 2011 SP1 HR2, as I never checked that.
But there is an open source version available on Google Code, which you can build with the Visual Studio Express edition (which you can download for free), and there you can specify different Core Service endpoints in the
web.config to make it work with your exact version of SDL Tridion.
Please note the latest version on Google Code is built against 2013 SP1, so you will need to change the Core Service endpoint and icon paths for 2011 SP1 HR2.
The ready built version is using
net.tcp://localhost:2660/CoreService/2011/netTcp as a Core Service endpoint. I believe that should still be correct for 2011 SP1 HR2, but ofcourse it does mean that it only works directly on the COntent Manager Server itself (as it is using a
net.tcp endpoint address).
This all being said, I would think the ready built version should work for you, but it is impossible for me to say what is going wrong with the limited information I get from you atm.