An error occurred while attaching module (Dynamicweb.Frontend.Content)

System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.
   at Dynamicweb.Indexing.IndexHelper.GetInstanceLatestStatus(String repository, String index, String instance)
   at Dynamicweb.Indexing.IndexHelper.IsInstanceAvailable(IIndexProvider instance)
   at Dynamicweb.Indexing.Lucene.LuceneIndexProvider.get_IsAvailable()
   at System.Linq.Enumerable.IEnumerableWhereSelectIterator`2.MoveNext()
   at Dynamicweb.Indexing.Balancing.LastUpdated.GetInstance()
   at Dynamicweb.Indexing.Querying.QueryService.Query(IQuery query, QuerySettings settings)
   at Dynamicweb.QueryPublisher.Frontend.GetModuleContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)