Run-Time Check Failure #2 - Stack around the variable 'foobar' was corrupted.

I am receiveing the warning message in the subject of this post,
displayed in a message box when I build and run teh sample code below. I
am using VS2005, and am running on W2k.

I repeat the 'error/warning' message below:

Run-Time Check Failure #2 - Stack around the variable 'foobar' was
corrupted.

I would be grateful if anyone can help point out what I may be doing
wrong, since I have spent the entire evening trying to fgure it out - to
no avail....

Code snippet follows below:

typedef struct
{
    double *data;
    long size;
    long datasize;
    long ipos;
} MyArray;

typedef struct
{
    MyArray f1, f2, f3, f4, f5, f6, f7;
}MyStruct ;

static long MyAlloc(MyStruct *s1, long size)
{
    long i1, i2;
    double *data[7];

    if (!s1) return -1 ;

    for (i1 = 0; i1 < 7; i1++)
    {
        if ((data[i1] = (double *)calloc(size, sizeof(double))) == NULL)
        {
            for (i2 = i1 - 1; i2 >= 0; i2--)
                free(data[i2]);
            memset(s1, 0, sizeof(MyStruct));
            return (-2);
        }
    }

    s1->f2 = s1->f3 = s1->f4 = s1->f5 = s1->f6 = s1->f7 = s1->f1;
    s1->f1.data = data[0];
    s1->f2.data = data[1];
    s1->f3.data = data[2];
    s1->f4.data = data[3];
    s1->f5.data = data[4];
    s1->f6.data = data[5];
    s1->f7.data = data[6];

    return (0);
}

int main (int argc, char* argv[])
{
    Test();
}

void Test()
{
    MyStruct foobar = {0};
    MyAlloc(&foobar, 100);
    MyFree(&foobar);
}

I would really like to understand what is causing this problem ...