Since you have 2.612 on another machine, this will count as an install. In other words you have Microstusio on your old machine and on your desktop.
You have two options. You can get online and uninstall 4.20 from your desktop then install it on a machine with a good burner or you can remove 2.612 from your old show machine and contact MTU support and they will clear you to install 4.20 on a machine with a good burner.
In other words 4.20 will uninstall and reinstall without contacting MTU.
(If you remove 4.20 and reinstall it, you can then upgrade your 2.621 version to 4.20.
)
It all depends on which two machines you want Microstudio on.
I hope this helps
Jim
