In terms of plugin scanning getting any messages about not getting the correct information is OK and the plugs still work fine. But the best thing to do is to create a separate folder and only
copy the DLL's of the plugs you know will work and only need or want inside Mixbus into that folder. Just get it to scan in there only. You need to make sure the folder it is going to scan is correctly set. You need to got onto that dialog box that sets that. Erase the path that is there first then point to where your special Mixbus folder is and click on that. It will only scan in there. Good news, it erases previous scans and starts a fresh. Don't put any 64 bit plugs in your new folder either. You need to open all the plugs you put in there to make sure they do not crash Mixbus.
It will scan that folder much faster too. Try closing down and reopening after doing all that. After that when you go to insert a plugin, you will be presented with only the Harrison options and the plugs inside your folder only. You end up with a much tidier plug in menu.
It is best to prevent it from scanning your whole system. You will end up with a mess of plugs inside Mixbus and many it cannot open
(virtual instruments for example) or it will crash with some plugs for various reasons. It also takes a long time to scan your whole system too.