Schannell: Certificate received from the remote server was issued by an untrusted certificate authority
You're getting those errors because something is trying to connect to SQL Server via SSL, and you don't have a real (signed) certificate trusted by all parties involved.

By setting "Force Encryption" to Yes, you won't make the errors go away - actually, the opposite. You'll make the errors happen everywhere, because you're not fixing the root problem. Right now, only a few things are trying to connect via SSL, but you're about to make EVERYTHING connect via SSL, which means everything will throw those errors. Bad idea.

Instead, track down what's trying to connect via SSL. If it's happening at the same date/time every time, you can set up a trace, or figure out what servers are running batch jobs. Then, THAT server is the one that needs a real cert (as well as the SQL Server) - or just change that application's settings so that it's not trying to connect with SSL.