The given key was not present in the dictionary

Hello,

When I try to index a client's EPiServer site I often get the exception that the "given key was not present in the dictionary".  Does anyone know why the indexer job is throwing the exception?

Full error stack below.

Thanks

Danie

<exception><![CDATA[System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.

at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at EPiServer.Core.PageProviderBase.GetScatteredPages(IList`1 pageRefs, ILanguageSelector selector)
at EPiServer.Core.PageProviderBase.GetPagesBatched(IList`1 pageLinks, ILanguageSelector selector)
at EPiServer.DataFactory.GetPages(IList`1 pageLinks, ILanguageSelector selector)
at EPiServer.Find.Cms.PageDataExtensions.SearchSection(PageData page)
at EPiServer.Find.DelegateValueProvider`2.GetValue(Object target)
at EPiServer.Find.ClientConventions.FieldConventionBuilder`1.<>c__DisplayClass2.<>c__DisplayClass4.<ConvertBeforeSerializing>b__1(Object instance)
at EPiServer.Find.DelegateValueProvider.GetValue(Object target)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)
at EPiServer.Find.Api.BulkActionConverter.WriteJson(JsonWriter writer, Object value, JsonSerializer serializer)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeConvertable(JsonWriter writer, JsonConverter converter, Object value, JsonContract contract, JsonContainerContract collectionContract, JsonProperty containerProperty)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)
at EPiServer.Find.Json.Serializer.SerializeToStringBuilder(JsonSerializer serializer, Object value, StringBuilder buffer)
at EPiServer.Find.Api.BulkCommand.Execute()
at EPiServer.Find.Client.Index(IEnumerable objectsToIndex)
at EPiServer.Find.Cms.PageIndexer.Index(IEnumerable`1 pages, IndexOptions options)