Maybe the ISO file was corrupted during you copy it to the USB key.
Here is the correct md5sum value https://github.com/rescuezilla/rescuezilla/releases
md5sum:
3f9753a949ef215eadf6afcad84dcce5 rescuezilla-2.1.3-64bit.groovy.iso
Here is the correct md5sum value https://github.com/rescuezilla/rescuezilla/releases
md5sum:
3f9753a949ef215eadf6afcad84dcce5 rescuezilla-2.1.3-64bit.groovy.iso