There are some apps called 'Device administrators'. These cannot be uninstalled from application list. All the details of these applications are greyed out - they neither can be force stopped nor uninstalled. Uninstalling from Google Play Store does not work as well.
I encoutered an app like this in Android 4.0 ICS called "Screen Timeout" that lets you set the screen timeout not only to the standard values. Unfortunately this app was buggy and crashed on ICS.
To uninstall an app like this just:
Go to: home screen->Menu->Settings->Security->Select Device Administrators
Find the application.
Then uncheck it from device administrators.
From now on the app can be force closed and uninstalled from the application list without any problems.