This is the error:
[AssemblyUpdater] Assembly reference folder does not exist: 'C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETPortable\v4.6\'
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: 'System.Runtime, Version=4.0.10.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
at Mono.Cecil.BaseAssemblyResolver.Resolve (Mono.Cecil.AssemblyNameReference name, Mono.Cecil.ReaderParameters parameters) [0x00000] in <filename unknown>:0
at Mono.Cecil.BaseAssemblyResolver.Resolve (Mono.Cecil.AssemblyNameReference name) [0x00000] in <filename unknown>:0
at Mono.Cecil.DefaultAssemblyResolver.Resolve (Mono.Cecil.AssemblyNameReference name) [0x00000] in <filename unknown>:0
at Mono.Cecil.MetadataResolver.Resolve (Mono.Cecil.TypeReference type) [0x00000] in <filename unknown>:0
at Mono.Cecil.ModuleDefinition.Resolve (Mono.Cecil.TypeReference type) [0x00000] in <filename unknown>:0
at Mono.Cecil.TypeReference.Resolve () [0x00000] in <filename unknown>:0
at Mono.Cecil.Mixin.CheckedResolve (Mono.Cecil.TypeReference self) [0x00000] in <filename unknown>:0
at Mono.Cecil.SignatureReader.ReadCustomAttributeEnum (Mono.Cecil.TypeReference enum_type) [0x00000] in <filename unknown>:0
at Mono.Cecil.SignatureReader.ReadCustomAttributeElementValue (Mono.Cecil.TypeReference type) [0x00000] in <filename unknown>:0
at Mono.Cecil.SignatureReader.ReadCustomAttributeElement (Mono.Cecil.TypeReference type) [0x00000] in <filename unknown>:0
at Mono.Cecil.SignatureReader.ReadCustomAttributeFixedArgument (Mono.Cecil.TypeReference type) [0x00000] in <filename unknown>:0
at Mono.Cecil.SignatureReader.ReadCustomAttributeConstructorArguments (Mono.Cecil.CustomAttribute attribute, Mono.Collections.Generic.Collection`1 parameters) [0x00000] in <filename unknown>:0
at Mono.Cecil.MetadataReader.ReadCustomAttributeSignature (Mono.Cecil.CustomAttribute attribute) [0x00000] in <filename unknown>:0
at Mono.Cecil.CustomAttribute.<Resolve>b__2 (Mono.Cecil.CustomAttribute attribute, Mono.Cecil.MetadataReader reader) [0x00000] in <filename unknown>:0
at Mono.Cecil.ModuleDefinition.Read[CustomAttribute,CustomAttribute] (Mono.Cecil.CustomAttribute item, System.Func`3 read) [0x00000] in <filename unknown>:0
at Mono.Cecil.CustomAttribute.Resolve () [0x00000] in <filename unknown>:0
at Mono.Cecil.CustomAttribute.get_ConstructorArguments () [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Visitor.Visit (Mono.Cecil.CustomAttribute customAttribute, Unity.Cecil.Visitor.Context context) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Visitor.Visit (Mono.Cecil.TypeDefinition typeDefinition, Unity.Cecil.Visitor.Context context) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Visitor.Visit (Mono.Cecil.ModuleDefinition moduleDefinition, Unity.Cecil.Visitor.Context context) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Visitor.Visit (Mono.Cecil.AssemblyDefinition assemblyDefinition, Unity.Cecil.Visitor.Context context) [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Visitor.Visit[AssemblyDefinition] (Mono.Cecil.AssemblyDefinition node, Unity.Cecil.Visitor.Context context) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Extensions.DoAccept[AssemblyDefinition] (Mono.Cecil.AssemblyDefinition definition, Unity.Cecil.Visitor.Visitor visitor) [0x00000] in <filename unknown>:0
at Unity.Cecil.Visitor.Extensions.Accept (Mono.Cecil.AssemblyDefinition assemblyDefinition, Unity.Cecil.Visitor.Visitor visitor) [0x00000] in <filename unknown>:0
at AssemblyUpdater.Steps.AssemblyUpdaterStepBase.Apply (AssemblyUpdater.Core.AssemblyUpdaterContext context) [0x00000] in <filename unknown>:0
at AssemblyUpdater.Core.AssemblyUpdaterPipeline.RunUpdateRound (AssemblyUpdater.Core.AssemblyUpdaterContext context) [0x00000] in <filename unknown>:0
at AssemblyUpdater.Core.AssemblyUpdaterPipeline.Run (AssemblyUpdater.Core.AssemblyUpdaterContext context) [0x00000] in <filename unknown>:0
at AssemblyUpdater.Application.Program.CheckForObsoleteAPIUsage (AssemblyUpdater.Application.CommandLineSpec config) [0x00000] in <filename unknown>:0
at AssemblyUpdater.Application.Program.Main (System.String[] args) [0x00000] in <filename unknown>:0
UnityEditor.Scripting.APIUpdaterHelper:DoesAssemblyRequireUpgrade(String)
How do I fix it?