Don’t know if you got it right by now, but here it goes how I solved it.
I write another thread in BUGS, about this.
It has to do with the way the script fog.download counts partitions.
If you really need multicast with multiple partitions:

unzip init.xz (the same goes for init32.xz) with xz -d init.xz mount the init file in a loop device with: mount -o loop init sometempdir/ go to sometempdir/bin with cd edit fog.download, and search for the part that does the multicast write, for your “method” (mps or mpa) look for the part that does a loop on each partition, and fix it in a way that it checks for the existence of the file
(something like if [ ! -f $imgpart ] ; then echo “Partition file missing …jumping”; sleep 1; else writeMulticastImage; fi )
(look in the “not multicast” lines or the previous multicast method, for just linux type) save your file, and back to the init file dir. zip it with xz -C crc32 init

Put the task again to try it.

Try it again …you should briefly the message “Partition file …” and get the correct ones to the partclone/partimage program stream

Other related bug is in the MulticastTask.class.php. If you have 10 or more partitions, you need natsort() instead of sort().

Maybe you need a (not so much experienced) linux shell programmer to help.

P.S. Be sure to have also installed the php-process extensions to PHP, as the killing of multicast tasks uses posix_ functions in it. (That is for a CentOS / Redhat server; on Ubuntu server I have not tested or searched for them)