m not able to write into ftp log file using this script

That's because, unless I missed something (it is a long program) then that's because the program is only reading the file, it does not appear to be designed to write to it.

It appears that the program is attempting to read a log file created by another program, which is a daemon. I think you are saying that the format has changed between operating systems. No surprise there. You need to get the specification of the new log file format (presumably from your supplier) and rewrite the program to conform to that.