Hoooooooooooooooooooo boy! This is going to be a long topic.
Firstly, you need to run the correct IOS version. What is the output of the "sh version"?
Next, what firmware version of the controller are you running?
The link below will give you the specific "how-to's" regarding configuring the WLC 2100. All you need is to determine the version of the firmware you are running and match the version of the Configuration Guide.
http://www.cisco.com/en/US/products/ps7206/products_installation_and_configuration_guides_list.html
The link below gives you the Release Notes. It's a summary at what the specific version of firmware you are running with a list of new features added, bugs, gotchas, and more. Have a look see.
Let us know if you run into more troubles.
By the way, Cisco is recommending everyone to stay away from 5.X and 6.X firmwares. Either stay with the 4.X or upgrade to the 7.X if possible.
Hope this helps. Please don't forget to rate useful posts. Thanks.