Developer forum

This error is being logged in the Event Viewer when this happens.

Index: Products
Date: 5/6/2016 8:22:42 AM
Solution: www.xxx.com
Error message: The process cannot access the file 'd:\Dynamicweb\Sites\www.xxx.com\Files\System\_search\Products\backup\_1a.fdt' because it is being used by another process.
Call stack:    at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.File.InternalDelete(String path, Boolean checkHost)
   at Dynamicweb.Searching.IndexInfo.<>c__DisplayClass2.<DeleteIndex>b__1()
   at Dynamicweb.Searching.IndexInfo.DeleteIndex()
   at Dynamicweb.Searching.Management.IndexUpdater.Update(IndexUpdateParameters parameters)
   at Dynamicweb.Searching.Indexer.PerformIndexModifications(IndexUpdateParameters parameters, IEnumerable`1 data, IndexModificationResult addToResult)
   at Dynamicweb.Searching.Indexer.PerformIndexModifications(IEnumerable`1 fromEntries, IndexUpdateParameters parameters)
   at Dynamicweb.Searching.Indexer.PerformUpdate(IEnumerable`1 data, IndexerQueueContentType expectedContentType, IndexUpdateParameters parameters)
   at Dynamicweb.Searching.IndexManager.UpdateIndexInternal(Indexer i, Boolean isFullUpdate, Boolean updateSpell, IDictionary`2 flags)

Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="ASP.NET 4.0.30319.0" />
    <EventID Qualifiers="16384">1132</EventID>
    <Level>2</Level>
    <Task>31337</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2016-05-06T12:22:42.000000000Z" />
    <EventRecordID>700875</EventRecordID>
    <Channel>Application</Channel>
    <Security />
  </System>
  <EventData>
    <Data>An error occured while updating an index.

I was able to resolve this by recycling the application pool but need to ensure it doesn't happen again.

Thanks for the information Nicolai.