Hi Annick !
I'll explain first why you got the error.
The assignment time: ���05:45��� failed because you tried to put an array of char (of size 5*sizeof(char)) inside an address.
At some point, you need to allocate the memory that will hold the data. In your case, you can do it quite easily with the class-side method #fromString: of class NBExternalAdress. This will return a pointer, which you can assign to the field of your struct.
Regarding what you really want to do, having a char[5] field in your struct, I'm not totaly sure how you can do it with NativeBoost. A C struc is just a chunk of memory with a well defined size, so if you want to specify a field as a char[5], you must have a type that match that size. It does not look like the field parser of NBExternalStruct can do it dynamicaly. You could maybe hard code it by subclassing NBExternalType into NBExternalArrayOf5Char, with a valueSize of 5.
As a final word, be wary of where you have allocated your objects, whether it is in object-space (#new), or in C heap (#externalNew). The first is garbage collected so the address are volatile, but you bare the duty of freeing the memory in the second.