In the first block of code you posted, the SeekFile is after the WriteInt. Also, after you write the integer, you're trying to seek from the current file position (end of file) then adding 4 bytes (past the end of file). The opposite to the second block of code.
I'm confused, if all you want to achieve is writing an integer over an entire file, why not just use WriteFile instead of OpenFile?
I'm confused, if all you want to achieve is writing an integer over an entire file, why not just use WriteFile instead of OpenFile?