There are two hacks available for Mackie OS 5.1. One of them requires activation codes, the other one does not.
So, if it asks for an activation code now, it looks like you’re using “Hack 1” (the one that needs codes).
It’s hard to tell what actually happened, but “something” changed on the hard drive, where the reference between the ESN and the entered serial number is stored. This “could” be a hiccup, but it could also mean that your hard drive (or CF card) has a problem. If it’s a spinning drive, I’d take that as an opportunity to replace it with a CF card adapter and CF card.
If the hard drive is NOT dying, and this was just a fluke, then I think the easiest way to resolve this issue, is to install “Hack 2” instead of “Hack 1."
Hack 2 doesn’t require any serial codes to be entered, but it unlocks all the plug-ins that exist for the D8B, anyway (for some, you need the right FX card to be installed for them to work… but the licenses for the plug-ins will be unlocked).
Hack 2 is much easier to apply than Hack 1. You just replace the file “MackieOS.exe” on your hard drive, with the version from Hack 2… restart, and things should work again.
However, if there IS a problem with the hard drive or CF, then there’s a good chance that there will still be other issues after replacing that MackieOS.exe file. In that case, it would likely be best to erase everything on that drive and re-install fresh (…and if going down that route, you might as well switch to a CF, if you haven’t, already).
Here’s a link to the thread/post where you can download Hack 2. The MackieOS.exe file is part of the zip file that is attached to this post:
https://d8bforum.com/phpBB3/viewtopic.php?f=2&t=1634&hilit=hack+2&start=150Best of luck!