I assume you have tried CHDK-DE before. That distribution contains a script named "default.lua", you managed to start that instead of shooting (this would explain the error message).
When you're in ALT mode ("ALT" is shown at the bottom of the screen), the camera buttons behave differently (as in your case, the shoot button in ALT mode starts the currently selected script).
When you get out of ALT mode, the camera buttons will work as normal (except for the button / button combination that is used as "ALT" button).
