The info in the FSB file is wrong. It says that the kernel starts at sector 3 and has a length of 2 sectors. This means it occupies the sectors 3 and 4. But then looking at the CHSL info for the INT21 file I see that it starts at sector 4 and also has a length of 2 sectors! Both files can't be in the same sector. You should change the sector component of the position of INT21 to a 5 and you should also not forget to account for the extra space in the number of free blocks:
2876(2880) --> 2874(2880)
The info in the FSB file is wrong. It says that the kernel starts at sector 3 and has a length of 2 sectors. This means it occupies the sectors 3 and 4. But then looking at the CHSL info for the INT21 file I see that it starts at sector 4 and also has a length of 2 sectors! Both files can't be in the same sector. You should change the sector component of the position of INT21 to a 5 and you should also not forget to account for the extra space in the number of free blocks: 2876(2880) --> 2874(2880)