>...What is the errno=28?...

Refer to your AIX documentation, or /usr/include/sys/errno.h specifically.

ENOSPC          28      No space left on device.
                        A write to an ordinary file, the creation of a directory
                        or symbolic link, or the creation of a directory entry
                        failed because no more disk blocks are available on the
                        file system, or the allocation of an inode for a newly
                        created file failed because no more inodes are available
                        on the file system.
                        In an AIX JFS enabled for Large Files, free space
                        fragmentation may be the problem:  Large disk blocks
                        require 32 contiguous 4KB blocks. If you write to large
                        files beyond the 4MB, file offset will fail with ENOSPC
                        if the file system does not contain 32 unused contiguous
                        4KB blocks.  Note: The file system may have thousands of
                        free blocks, but if 32 of them are not contiguous, the
                        allocation will fail.  The defragfs command reorganizes
                        disk blocks to provide larger contiguous free block
                        areas.  Ref: InfoExplorer "Understanding Large Files".

  Richard Sims, BU