You might encounter this error message in XenServer when launching a VM:
This VM needs storage that cannot be seen from that server
I am not sure why the guys over at Citrix decided to refer to the host you are trying to launch the VM on as “that server”, but this error message simply means that your host cannot access the SR this VM is stored on. This usually means that the SR go detached for some reason, and it is very likely that the SR is going to show up as unplugged in XenCenter, and trying to repair it from the XenCenter client would return another error message, typically something like this:
Error parameters: , Logical Volume mount/activate error
The first result in Google if you try to look for the error message in the title of the post brings you to a post on the Citrix Discussion website recommending to eject any disc from the DVD drive of the VM, but in my case there was no disc inserted, so this wasn’t helpful. What worked for me was removing the SR and adding it back to XenServer. I then restored my VM metadata so that all the drives could be attached to the correct VMs once again.