1: Product Name: SSG5-ISDN
Software Version: 6.3.0r22.0 <-- this means device is already on the latest version.
2 :ssg5-isdn -> save software from tftp 192.168.XX.XX Loadssg5ssg20v132.d to flash // bootloader upgrade
If you are getting software error during the bootloader upgrade then it looks to be fine because this is not how you should upgrade the bootloader.
Please follow KB https://kb.juniper.net/InfoCenter/index?page=content&id=KB10949&smlogin=true&actp=search to upgrade the bootloader.
Thanks,
Vikas