not found [No such file or directory] error, even though the file present in that directory on RH Linux 6.2

not found [No such file or directory] error, even though the file present
in that directory on RH Linux 6.2

When I'm executing a script from Linux(RH Linux 6.2), it is giving not
found [No such file or directory] error, even though the file present in
that directory (checked the permissions and they are fine).
Example:
md1silinux04:/data/upgrade> /data/upgrade/upgrade_db.ksh -ksh:
/data/upgrade/upgrade_db.ksh: not found [No such file or directory]
md1silinux04:/data/RAIL/rpo402/db/upgrade> ls /data/upgrade/upgrade_db.ksh
/data/upgrade/upgrade_db.ksh
Could anybody please help on this ?