After switching the TargetServerVersion in Visual Studio to SQL Server 2012, I received the following error message. (This is reproduceable in VS2019 and VS2017.)
"Object reference not set to an instance of an object"
Resolution: Please check if you have duplicate mappings in the DTS folders under C:\Program Files (x86)\Microsoft SQL Server\, as Visual Studio doesn't handle such errors gracefully. A quick way to do that is to add the problematic package that targets SQL Server 2012 to a project that targets a later version (e.g. SQL Server 2019) and inspect the popup that shows a list of warnings.
NOTE: Some of our clients have had problems with the KinsgwaySoft components. If you see a warning about duplicate KinsgwaySoft mappings, please remove KingswaySoft.UpgradeMapping.*.xml files residing in folders C:\Program Files (x86)\Microsoft SQL Server\vvv\DTS\UpgradeMappings where vvv is 110, 120, 130, 140, 150.