The cause of the reported access violation was not forced by calling GetInventoryItem. Before this i do a function call for:

FFACE_API void GetItemNameByID(short index, void *buffer, int *size, DWORD PID = 0 );

Strange about it is, that depending upon the mapping I do get or not get an access violation. The mapping causing it looks like this:

void GetItemNameByID(short index, PointerByReference buffer, IntByReference size, int PID);