Swashbuckle.WebApi: MissingMethodException

I’m getting the following exception when before everything was working fine:

500 : {"ClassName":"System.MissingMethodException","Message":"Method not found: \"System.Func2<System.String,System.String> Newtonsoft.Json.Serialization.JsonDictionaryContract.get_PropertyNameResolver()".“,“Data”:null,“InnerException”:null,“HelpURL”:null,“StackTraceString”:” bei Swashbuckle.Swagger.SchemaRegistry.<>c__DisplayClass18.<CreateDictionarySchema>b__14(String name)\r\n bei System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer)\r\n bei Swashbuckle.Swagger.SchemaRegistry.CreateDictionarySchema(JsonDictionaryContract dictionaryContract)\r\n bei Swashbuckle.Swagger.SchemaRegistry.CreateInlineSchema(Type type)\r\n bei Swashbuckle.Swagger.SchemaRegistry.<CreateObjectSchema>b__1f(JsonProperty prop)\r\n bei System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer)\r\n bei Swashbuckle.Swagger.SchemaRegistry.CreateObjectSchema(JsonObjectContract jsonContract)\r\n bei Swashbuckle.Swagger.SchemaRegistry.CreateDefinitionSchema(Type type)\r\n bei Swashbuckle.Swagger.SchemaRegistry.GetOrRegister(Type type)\r\n bei Swashbuckle.Swagger.Annotations.ApplySwaggerResponseAttributes.Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)\r\n bei Swashbuckle.Swagger.SwaggerGenerator.CreateOperation(ApiDescription apiDesc, SchemaRegistry schemaRegistry)\r\n bei Swashbuckle.Swagger.SwaggerGenerator.CreatePathItem(IEnumerable1 apiDescriptions, SchemaRegistry schemaRegistry)\r\n bei System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer)\r\n bei Swashbuckle.Swagger.SwaggerGenerator.GetSwagger(String rootUrl, String apiVersion)\r\n bei System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory)\r\n bei AboServer.API.Config.SwaggerCachingProvider.GetSwagger(String rootUrl, String apiVersion)\r\n bei Swashbuckle.Application.SwaggerDocsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)\r\n bei System.Net.Http.HttpMessageInvoker.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)\r\n bei System.Web.Http.Dispatcher.HttpRoutingDispatcher.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)\r\n bei System.Net.Http.DelegatingHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)\r\n bei AboServer.API.Handlers.SessionHandler.<SendAsync>d__1.MoveNext()","RemoteStackTraceString":null,"RemoteStackIndex":0,"ExceptionMethod":"8\n<CreateDictionarySchema>b__14\nSwashbuckle.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=cd1bb07a5ac7c7bc\nSwashbuckle.Swagger.SchemaRegistry+<>c__DisplayClass18\nSystem.String <CreateDictionarySchema>b__14(System.String)","HResult":-2146233069,"Source":"Swashbuckle.Core","WatsonBuckets":null,"MMClassName":null,"MMMemberName":null,"MMSignature":null} http://myserver:80/myapp/swagger/docs/v1