Hey guys,
I started having the same problem as Eric but not after upgrading, in fact out of the blue. I have been working on with this computer for a few years now (Mac Pro 2013 6-core). The only change recently was upgrading to Sierra, but this was more than a month ago. I have produced many projects in Logic since then. And yesterday out of the blue I started having this problem.
It starts like this: I start logic normally. Work a little bit, when I try saving, I will get the beachball of death and have to force quit Logic. When I start it again then I get the updating info on audio units and get the dialogue on midi initialization error.
Then the only thing that makes Logic start normally again is restarting the computer.
Well, obviously I can't restart my computer every time I need to save a project, I will get crazy.
Any ideas how to troubleshoot it?
Thanks!