I'm trying to implement a custom search on Umbraco Examine. When I modify the ExamineSettings.config I get this error:

Error: Parameter name indexset on Lucene Examine Indexer provider has not been set in configuration and / or the IndexerData property has not been explicitly set.

I am using the following:

ExamineSettings.config

<?xml version="1.0"?>
<!-- 
Umbraco examine is an extensible indexer and search engine.
This configuration file can be extended to add your own search/index providers.
Index sets can be defined in the ExamineIndex.config if you're using the standard provider model.

More information and documentation can be found on GitHub: https://github.com/Shazwazza/Examine/
-->
<Examine>
  <ExamineIndexProviders>
    <providers>
      <add name="InternalIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine" supportUnpublished="true" supportProtected="true" analyzer="Lucene.Net.Analysis.WhitespaceAnalyzer, Lucene.Net" directoryFactory="Examine.LuceneEngine.Directories.SyncTempEnvDirectoryFactory, Examine" />

      <add name="InternalMemberIndexer" type="UmbracoExamine.UmbracoMemberIndexer, UmbracoExamine" supportUnpublished="true" supportProtected="true" analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net" directoryFactory="Examine.LuceneEngine.Directories.SyncTempEnvDirectoryFactory, Examine" />

        <!-- default external indexer, which excludes protected and unpublished pages-->
        <add name="ExternalIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine" directoryFactory="Examine.LuceneEngine.Directories.SyncTempEnvDirectoryFactory, Examine" />

      <!-- Wright Hassall Index Providers -->
      <add name="RelatedLegalArticlesIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine"/>

    </providers>
  </ExamineIndexProviders>

  <ExamineSearchProviders defaultProvider="ExternalSearcher">
    <providers>
      <add name="InternalSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine" analyzer="Lucene.Net.Analysis.WhitespaceAnalyzer, Lucene.Net" />

      <add name="ExternalSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine" />

      <add name="InternalMemberSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine" analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net" enableLeadingWildcard="true" />

        <!-- Wright Hassall Search Providers -->
        <add name="RelatedLegalArticlesSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine" analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net"/> 

    </providers>
  </ExamineSearchProviders>

</Examine>

ExamineIndex.config

<?xml version="1.0"?>
<!-- 
Umbraco examine is an extensible indexer and search engine.
This configuration file can be extended to create your own index sets.
Index/Search providers can be defined in the UmbracoSettings.config

More information and documentation can be found on GitHub: https://github.com/Shazwazza/Examine/
-->
<ExamineLuceneIndexSets>
  <!-- The internal index set used by Umbraco back-office - DO NOT REMOVE -->
  <IndexSet SetName="InternalIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/Internal/" />

  <!-- The internal index set used by Umbraco back-office for indexing members - DO NOT REMOVE -->
  <IndexSet SetName="InternalMemberIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/InternalMember/">
    <IndexAttributeFields>
      <add Name="id" />
      <add Name="nodeName" />
      <add Name="updateDate" />
      <add Name="writerName" />
      <add Name="loginName" />
      <add Name="email" />
      <add Name="nodeTypeAlias" />
    </IndexAttributeFields>
  </IndexSet>

  <!-- Default Indexset for external searches, this indexes all fields on all types of nodes-->
  <IndexSet SetName="ExternalIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/External/" />

  <!-- Wright Hassall Custom Index Set -->
  <IndexSet SetName="RelatedLegalArticlesIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/RelatedLegalArticles/"> 
    <IndexAttributeFields> 
    <add Name="id" /> 
    <add Name="nodeName" /> 
    <add Name="updateDate" /> 
    <add Name="writerName" /> 
    <add Name="path" /> 
    <add Name="nodeTypeAlias" /> 
    <add Name="parentID" /> 
    </IndexAttributeFields> 
    <IndexUserFields> 
    <add Name="pageAuthors"/> 
    </IndexUserFields> 
    <IncludeNodeTypes> 
    <add Name="legalArticle"/> 
    </IncludeNodeTypes> 
    <ExcludeNodeTypes> 
    </ExcludeNodeTypes> 
    </IndexSet> 

</ExamineLuceneIndexSets>

I'm not sure what I'm doing wrong here? Any ideas would be gratefully received.