Failed to resolve assembly Xamarin.IOS in Visual Studio – Visual Studio

I received the following message when deploying after updating my version of Xamarin

Severity	Code	Description	Project	File	Line	Suppression State
Error		Failed to resolve assembly: 'Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065'
   at Mono.Cecil.BaseAssemblyResolver.Resolve(AssemblyNameReference name, ReaderParameters parameters)
   at Mono.Cecil.DefaultAssemblyResolver.Resolve(AssemblyNameReference name)
   at Mono.Cecil.MetadataResolver.Resolve(TypeReference type)
   at Mono.Cecil.TypeReference.Resolve()
   at Mono.Cecil.Mixin.CheckedResolve(TypeReference self)
   at Mono.Cecil.SignatureReader.ReadCustomAttributeEnum(TypeReference enum_type)
   at Mono.Cecil.SignatureReader.ReadCustomAttributeElementValue(TypeReference type)
   at Mono.Cecil.SignatureReader.ReadCustomAttributeElement(TypeReference type)
   at Mono.Cecil.SignatureReader.ReadCustomAttributeFixedArgument(TypeReference type)
   at Mono.Cecil.SignatureReader.ReadCustomAttributeConstructorArguments(CustomAttribute attribute, Collection`1 parameters)
   at Mono.Cecil.MetadataReader.ReadCustomAttributeSignature(CustomAttribute attribute)
   at Mono.Cecil.CustomAttribute.<Resolve>b__2(CustomAttribute attribute, MetadataReader reader)
   at Mono.Cecil.ModuleDefinition.Read[TItem,TRet](TItem item, Func`3 read)
   at Mono.Cecil.CustomAttribute.Resolve()
   at Mono.Cecil.CustomAttribute.get_ConstructorArguments()
   at Mono.Cecil.ImmediateModuleReader.ReadCustomAttributes(ICustomAttributeProvider provider)
   at Mono.Cecil.ImmediateModuleReader.ReadMethods(TypeDefinition type)
   at Mono.Cecil.ImmediateModuleReader.ReadType(TypeDefinition type)
   at Mono.Cecil.ImmediateModuleReader.ReadTypes(Collection`1 types)
   at Mono.Cecil.ImmediateModuleReader.ReadModule(ModuleDefinition module)
   at Mono.Cecil.ModuleWriter.WriteModuleTo(ModuleDefinition module, Stream stream, WriterParameters parameters)
   at Mono.Cecil.ModuleDefinition.Write(Stream stream, WriterParameters parameters)
   at Mono.Cecil.ModuleDefinition.Write(String fileName, WriterParameters parameters)
   at Xamarin.Build.Download.XamarinBuildiOSResourceRestore.MergeResources(IAssemblyResolver resolver, String originalAsmPath, String mergedAsmPath, List`1 resourceItems)	CanadianClassifiedsAlerter.iOS

After verifying both my build server and development machine were running the same version of Xamarin, I noticed a slight hint at the end of the message

 at Xamarin.Build.Download.XamarinBuildiOSResourceRestore

Solution

I fixed it by updating Xamarin.Forms and Xamarin.Build.Download in both my Portable project and the iOS project and it built just fine 🙂

It’s that easy.