Android emulator error: "Device error: System.ComponentModel.Win32Exception (0x80004005): The specified executable is not a valid..."

Android emulators worked fine for a long time till today. I suddenly started getting the following error:

Device error: System.ComponentModel.Win32Exception (0x80004005): The specified executable is not a valid application for this OS platform.
   at System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo)
   at Xamarin.DeviceManager.Common.EmulatorManager.<>c__DisplayClass61_0.<StartProcess>b__0()

I checked a similar post and tried its solution. aapt.exe in directory "C:\Program Files (x86)\Android\android-sdk\build-tools\28.0.3" is fine. I have rebooted Visual Studio and restarted my PC to no avail. I am wondering if anyone could offer a tip on how to remedy this.