[syslinux] ext4, boot error after writing irrelevant files on same partition

[Denys Fedoryshchenko]

Hi!

I faced very strange problem, after i install extlinux, on ext4 
partition and i wrote some files (they doesn't touch syslinux files), 
system refuse to boot and gives "Boot error".
I checked ldlinux.sys, file is fine, checksum is intact and etc.
Running extlinux -i /mountpoint sure fixes the problem.

What are the steps to troubleshoot the problem?

Thanks