This can be caused by creating a file or directory name under $FWDIR or $CPDIR that has an embedded space or other illegal character in it. When the tar or gzip is happening in those directories the embedded space causes the parsing of command line options to fail and produces an error message like you are seeing. Try running this command:
find / -name "*\ *" -print
(There is a space between the backslash and the second asterisk)
Note that there are numerous files that legitimately have a space in them that are part of the standard Check Point software distribution (such as for DLP), but be on the lookout for files or directories in this output created by administrators that contain packet captures, cpinfos, debug outputs, etc. Delete those and it should enable the backup to successfully run.
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