SLathaJ, a
du -ak | sort -n
in the root of the filesystem will tell you the actual size of all files down the directory tree and sort it so the largest sized files is at the end. You might find the offending file there.
I usually use du -sk * | sort -n, which will narrow it down by file and directory and then go from there. An ls -l can be deceiving on the amount of space you will gain by deleting a file.
Check for a core file in the filesystem (cd <filesystem> and then find . -name core).
Also, I seem to recall that in some Unix OS's a runaway process or an inode that can't be released is the offender. I don't know if that happens in AIX.