When I installed .net 4.5.1 on my windows server 2012 (version 6.2 build 9200), all sql server connections were broken. Any time I tried to connect to the sql server, I'd see an error stating:
The message received was unexpected or badly formatted.
I also saw this C++ runtime error in some programs like linqpad and SSMS:
r6025 pure virtual function call
This caused app pools in IIS to completely stop for any site connecting to sql server.
When I finally uninstalled .net 4.5.1, connectivity to sql server was restored, but applications requiring that version of .net fx were out of commission.
Google and event logs haven't turned up anything useful for how I should proceed to get .net 4.5.1 on this machine.