I ran the offline upgrade from SLES 11.4 to 12.3 - that far it worked but now I have this very tiresome issue:

It is a VM installed on XenServer 7.5 and I cannot boot the VM. XenServer aborts with

Internal error: xenopsd internal error: VM = xxx; domid = 29; Bootloader.Bad_error [Errno 2] No such file or directory.

Good, may be this is a XenServer issue but I want to assure it isn't SLES.

BUT:
I can start the VM when I start the VM in the Recovery Mode and there I select the first option Boot from Hard Disk.
Isn't it strange?

I have the feeling it cannot be that much but it should be solved because I cannot always start this VM this way.