SQL Server 2012 error: object reference not set to an instance of an object

Question

I use SQL Server 2012 and I have some databases on it. The problem is I suddenly get an error saying,

object reference not set to an instance of an o

Answer 1

I got the same error for SQL 2016 and the only solution for me was to completely uninstall (in appwiz.cpl) all entries Visual Studio + SQL. Then I executed VisualStudioUninstaller and I reinstalled SQL and after Visual Studio.