The tools version "15.0" is unrecognized. Available tools versions are "14.0", "2.0", "3.5", "4.0"

從VisualStudio 2017 升級安裝 VisualStudio 2019 時，常常在執行舊有或者建位新專案時會出現下面的訊息：

「The tools version "15.0" is unrecognized. Available tools versions are "14.0", "2.0", "3.5", "4.0"」

這是因為在安裝時MsBuild相關的dll 會仍然有舊有的15.1版本的dllGAC。

所以解決的方式是以管理員身份執行Visual Studio Developer Command下指令去移除舊有的Dll版本，如下圖：

執行以下命令來移除Microsoft.Build.*.dll 15.1版本：

gacutil.exe /u "Microsoft.Build.Framework, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

gacutil.exe /u "Microsoft.Build, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

gacutil.exe /u "Microsoft.Build.Utilities.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

gacutil.exe /u "Microsoft.Build.Engine, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

gacutil.exe /u "Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

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