After spending hours trying to open and use Quickbooks 2016 after the latest update, I found a work-around....
After spending hours trying to open and use Quickbooks 2016 after the latest update, I found a work-around. Apparently, these errors, 1601, and 1603 are "ongoing" according to the service rep and as of now, they don't have a fix.
I finally decided to try to roll back my computer to an earlier backup (windows backup, not quickbooks) and then reinstalled quickbooks. This time it worked. (I'd tried it about 6 times, with restarts, clean install, and all the other suggested fixes, as well as spending an hour on the phone with a representative who wasn't able to fix it)
I'm now able to open and use quickbooks. Hopefully, this will help someone else. Best of luck.