What operating system do you have?
Does it run on the same type of real server?
If VM it is Windows, you must reset (sysprep) or insert the hdd drivers. Acronis is a solution for that, or Dism++ and ImDisk to insert dirvers on vhd.
If VM it's Linux, you don't have the correct disk name or partition ID, the boot partition must be redone. Reinstall kernel, in chroot with live CD, to solve the problem.
For an easier process, I recommend Hyper-V -> VirtualBox -> XCP-ng. With VirtualBox you will have fewer problems when restoring the boot. And VirtualBox is much more compatible with XCP-ng.
@Kajetan321 I think there is a misunderstanding how the ISO repository works vs. the XO remotes.
The remotes on XO are connected to XO and not XCP. XO used them for backups, etc.
The ISO repository is connected to each XCP host server. You can't use an ISO on XCP that is accessible only by XO. So if XO has access to the ISOs it won't help because XCP needs direct access to them.
When you use an ISO to boot or mount in a VM it needs to be accessible to the XCP host and not the XO system.
So if you have a pool of 200 XCP hosts then you add the ISO repository (NFS share) to the pool once.
If you have 200 XCP hosts (not a pool of 200) then you need to add the shared ISO to each XCP host (or each pool that's a group of hosts).
@olivierlambert Yes, it seems so. The switches are of different brands between RACs and since a year ago the datacenter was divided in 2 companies and we are not sure how they have organized the networks.
Then I had another error but with "rescan all disks" on the host it was solved.
You should be able to go to the network tab for the VM, click the network it's currently connected to, and then change it to the new one. If you have the management tools installed this can be done live, otherwise you'd need to shut the VM down.