The Introjucer Tools like e.g. the 'UTF-8 String-Literal Helper' are shown in Introjucers own FloatingToolWindow.
This FloatingToolWindow has a minor flaw:
1. Open such a window.
2. Close it by using the esc-key.
-> The window can't be opened anymore. A restart of the Introjucer is required.
A quick fix would be to disable the esc-key functionality via the constructor argument of DialogWindow. But using escape to close such a window is very handy.