"two files are the same file/group number or the same file"
*Cause: There is an overlap of file numbers in the files specified on
the command line or the same file is specified twice. If they are
not the exact same file then one is likely to be a backup of the
other. If they are two members of the same log they must be specified
together in a group file spec. This message will also appear if
the same control file appears more than once in the control_files
parameter in the init.ora file. If this happens, check for
additional error messages.
*Action: Confirm that the file mentioned is not a repeat of a file already
mentioned in the command. If they are different files then omit the
earlier backup. If they are members of the same log, insure they are
in the same group file specification. If this message appears because
of a duplicate control file, check the control_files parameter in the
init.ora file and see if a file is specified more than once.
If all files names appear to be unique, check to make sure that the
actual control files themselves are unique. For example, in UNIX
check for a symbolic or a hard link to another control file in the list.