Eng:Error Catching

There was a system in Scratch 1.4 that detects scripting errors or other problems.

If, while running a project, The Scratch Program finds a mistake, it will attain a red border around the script and stop the program from running any further. The block (or blocks) causing the problem will turn red.

Causes
Errors can be caused by the following:
 * Dividing by zero
 * Using an invalid input in function block (operators)
 * Using a motion block in the Stage
 * Attempting to access the nth item of a list where n<0

Turning off Error Catching
To turn the Error Catching off, press the R in the Scratch logo while holding shift and press the "turn error catching off" option.