Are you sure you understand the format of the binary data that is included in the file? Your comments make it appear that there is more than on piece of binary data included, but you try and read in 12 bytes and then unpack it as an "I" (do your system and the data you are reading both consider integers to be 12 bytes long?)

You also indicate that you tried both "N" (big-endian unsigned long), and "I" (unsigned integer) which are really not compatible data types, if you don't know the format of the data being unpacked, you will have a difficult time finding the right template to unpack it.