'Unknown error' 0x80131700 on SQL databases plan

A SQL databases type plan may fail with result 0x80131700 'Unknown error'.

Upon investigation, it may be found that the server hosting the instance of SQL may not have .NET Framework 3.5 installed. To check, on the SQL Server open Server Manager > Manager > Add Roles and Features Wizard and click Next until the Features window displays.

If .NET Framework 3.5 Features is not checked, check the box and click Next and then Install. .NET Framework 2.0 is installed with 3.5 and is required for the SQLPlanLaunch executable to run the plan.