title: Xamarin Forms - iOS - error MT3001: Could not AOT the assembly
body: <p>Xamarin Forms iOS project was building yesterday 10/10/19. Updated to latest components on Mac &amp; Windows today, project no longer builds.</p>
  
  <p>Build: Release - iPhone - TestMobile.iOS - Device</p>
  
  <p>Project works on Mac simulator. Project deploys &amp; debugs on iPhone hardware.</p>
  
  <ul>
  <li>Visual Studio Pro 2019 - 16.3.4</li>
  <li>Visual Studio 2019 for Mac - 8.3.3
  build 8</li>
  <li>all components latest on Mac</li>
  <li>MacOS Catalina 10.15</li>
  </ul>
  
  <p>Build Log:</p>
  
  <pre><code>3&gt;  AOT Compilation exited with code 1, command:
  3&gt;  MONO_PATH=/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/32/3-Build /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/bin/arm-darwin-mono-sgen --debug -O=gsharedvt -O=-float32  --aot=mtriple=armv7-ios,data-outfile=/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/armv7/ZXingNetMobile.aotdata.armv7,static,asmonly,direct-icalls,full,soft-debug,dwarfdebug,no-direct-calls,outfile=/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/armv7/ZXingNetMobile.dll.s "/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/32/3-Build/ZXingNetMobile.dll"
  3&gt;  '/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C' in MONO_PATH doesn't exist or has wrong permissions.
  3&gt;  '/Temp/iOS/mtouch-cache/32/3-Build' in MONO_PATH doesn't exist or has wrong permissions.
  3&gt;  The assembly mscorlib.dll was not found or could not be loaded.
  3&gt;  It should have been installed in the `/Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/external/mono/sdks/out/ios-cross32-release/lib/mono/4.5/mscorlib.dll' directory.
  3&gt;  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang  -Wno-receiver-forward-class -Wno-objc-missing-super-calls -Wno-unguarded-availability-new -stdlib=libc++ -gdwarf-2 -std=c++14 -I/Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/SDKs/MonoTouch.iphoneos.sdk/usr/include -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.1.sdk -Qunused-arguments -miphoneos-version-min=8.0 -arch arm64 -c -o /Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/arm64/registrar.o -x objective-c++ -DDEBUG /Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/64/registrar.m
  
  3&gt;  C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(842,3): 
  error MT3001: Could not AOT the assembly '/Users/bob/Library/Caches/Xamarin/mtbs/builds/TestMobileXF.iOS/e5f1c3a4936492ad245f1c68c3157dfc/C:/Temp/iOS/mtouch-cache/64/3-Build/TestMobileXF.iOS.exe'
  </code></pre>
  
  <p>Tried iOS Build settings:</p>
  
  <ul>
  <li>Linker Behavior</li>
  <li>Supported Architectures</li>
  <li>LLVM compiler</li>
  <li>Incremental builds</li>
  </ul>
  
  <p>Reverting Visual Studio Pro 2019 is a last resort. Any ideas appreciated.</p>