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This means that there are (at least) two different question prototypes defining the octave_function question type, which is thus ambiguous and unusable. You need to delete all but one. 

The situation can arise if you import a set of questions that includes an octave_function prototype. Have you done any imports lately?

On a fresh install, CodeRunner loads all built-in prototypes into the category System/Top for System/CR_PROTOTYPES. There should be exactly one question named BUILTIN_PROTOTYPE_octave_function in that category. If you have Moodle admin rights, that's the first thing to check (only Moodle administrators can see the system-context questions). If there is only one such question in the system context, you then need to look within the course in which the issue is occurring for questions with the same name, or perhaps named just PROTOTYPE_octave_function.

There are other more complex ways to hunt down rogue prototypes but the above covers most situations. Post back if you still can't resolve the issue.

Richard