OK I have read in details the manual (script conversion) and programmed my function the same way :

#include "stdlib.h"

__declspec(dllexport) void basic_test (double a, double b, double *c)
{
double *out;

out = c;

*out = a + b;
}

I created the dll and placed it in the zorro folder, my zorro script is :

int __stdcall basic_test(double a, double b, double *c);
API(basic_test,bar)

function main()
{
double c;

basic_test(5.25, 5.25, &c);

printf("\nResult = %f", c);
}

when compiling I got the correct answer :

Result = 10.500000

but once again the same error message !!!!

Error111: Crash in script

this is driving me mad I cannot believe no one never encountered the same issue !