Well that's not relevant to WinSCP. It looks like a corrupted archive.
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
Command 'tar -xz --directory="." -f "backup_2014_06_12__18_23.tar.gz"'
failed with return code 2 and error message
tar: Archive value 17179869183 is out of time_t range -2147483648.2147483647
tar: mod/LeValidate/ColabReg.otf: implausibly old time stamp 1969-12-31 18:59:59
tar: templates/index.html: Cannot open: File exists
tar: templates/.htaccess: Cannot open: File exists
tar: templates: Cannot utime: Operation not permitted
tar: Error exit delayed from previous errors.