I have an authorized license of ArcServer running that doesn't expire until 2018.

I am attempting to make a database connection in ArcMap and I get this:

Thing is, I was able to make database connections from ArcMap about a month ago no problem, and I haven't touched the Server to upgrade or authorize or do any of that kind of thing at all over the past month. This also is only happening when I try to connect to one specific database on our SQL Server, the other ones connect no problem. When I insert the current keycodes file, the operation fails and gives me this error:

I don't understand why it will not connect to this database. Anybody have any ideas?
Using Desktop 10.5, ArcGIS Server 10.4.1, and somehow our SDE geodatabases (the ones I can connect to) are 10.3.1 when I look at "Upgrade status" in the database properties dialogue box.