What steps will reproduce the problem?
1. Quit iChm
2. Go to user's Library > Preferences folder and delete "com.robinlu.iChm.plist"
3. Open iChm.  Quit iChm.
4) Open iChm again.  Dialog appears, asking user "Check for updates automatically?"
5) Choose either "Don't check" or "Check automatically".
6) After choosing an option, the setting can no longer be changed.  User is no longer able to 
change the "Automatically check for update" setting.

What is the expected output? What do you see instead?
User should be able to change the "Automatically check for update" setting at any time.  But 
instead, this setting is only accessible once.  Afterwards, the user can no longer change it.

What version of the product are you using? On what operating system?
iChm Version 1.3.2 (2826260)
Mac OS 10.5.5