unprotected error in call to Lua API (13)

[Elie Michel <elie.michel@...>]

Is "13" really an error message?

My setup is a globally defined function, called many times from a C++ 
code. It works for the ~ 500 first calls and suddenly fails with this error.

Not easy to extract some simple example from my code, but I could 
consider doing it if this "13" has ne clearer meaning…

Thanks,
Élie