SLES12 SP5 mksusecd iso wont install

Get this error when building system from an iso created using mksusecd (from SLES12 SP5 install files) and put on a USB Stick:

To use selected repository a matching boot image is needed. Download repository, yes/no.

When I select yes, files are downloaded (from the install files on my USB stick, I suspect) and the installation continues.
Is there a way to avoid this - a switch to use with the mksusecd command (instsys or defaultrepo)? Anybody have an example?

I am creating my own iso because I add folders containing autoyast install files.

I have another way to do this that involves xorriso along with the first 512 bytes from the original iso but it seems like mksusecd would be better.

Thanks.

The resulting installed system was actually SP4 (per hostinfo). I am trying to create the USB install media for SP5 from a running SLES12 SP4 machine. Does mksusecd use the boot files from the installed system and not from the iso?

Problem turned out to be SP4 Install DVD in the drive (didn’t know it was there). Even though booted from USB stick and performed install using autoyast=usb:////autoinst.xml the installer seemed to default to looking for install files on the DVD and installed SP4. Solution was to remove the DVD, install from USB with no trouble. SP5 installed.