Cannot get a 64 bit version of isohybrid in 64 Bit Mint 19
 

I have tried to run MultiCD with a 64Bit Mint 19. It says
Could not run downloaded isohybrid (it's probably 32-bit) - looking for installed version...

I have it working on a 32 bit Mint 19 now so the problem is really isohybrid is only a 32 bit version.

Any ideas of loading a 64 bit version of isohybrid?

Have you tried contacting Mint and asking them?

Their email address is here: https://linuxmint.com/contactus.php

No found there is no 32 bit version you have to use a 32 bit operating system to make it work so I have two now on a 64 bit machine to solve this.