Could not load type 'Microsoft.Build.Framework.SdkReference' on project open in VS 2017 U1 (15.3)

Question

After doing an (apparently successful) upgrade from VS 2017 15.1 to 15.3, I can no longer load any C# project (can\'t open existing, can\'t create new). All fail with this e

Answer 1

Use an adminstrator "Developer Command Prompt for VS 2017" to run

gacutil /u "Microsoft.Build.Framework, Version=15.1"

Please do not reinstall another version to the GAC. MSBuild should not be in the GAC, and installing it there will cause problems the next time Visual Studio updates MSBuild, because the file from the GAC gets preferred over the updated version delivered with Visual Studio.