I have a site running Umbraco 4.7.1.1, with Examine indexing for search etc.  I didnt build it myself so dont know the details of how its configured, but occasionally all the macros stop working and the following error gets thrown in the umbraco log:

Error loading IApplication: System.Reflection.TargetInvocationException:
 Exception has been thrown by the target of an invocation. ---> 
System.TypeInitializationException: The type initializer for 
'Examine.ExamineManager' threw an exception. ---> 
System.Configuration.ConfigurationErrorsException: The process cannot 
access the file 
'C:\Inetpub\vhosts\...\App_Data\TEMP\ExamineIndexes\Internal\VMH12355.lck'
 because it is being used by another process. 
(C:\Inetpub\vhosts\...\config\ExamineSettings.config
 line 12) ---> System.IO.IOException: The process cannot access the 
file 
'C:\Inetpub\vhosts\...\App_Data\TEMP\ExamineIndexes\Internal\VMH12355.lck'
 because it is being used by another process.
   at System.IO.__Error.WinIOError(Int32 errorCode, String 
maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess 
access, Int32 rights, Boolean useRights, FileShare share, Int32 
bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String 
msgPath, Boolean bFromProxy, Boolean useLongPath)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess 
access, FileShare share, Int32 bufferSize, FileOptions options)
   at System.IO.StreamWriter.CreateFile(String path, Boolean append)
   at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding
 encoding, Int32 bufferSize)
   at System.IO.StreamWriter..ctor(String path, Boolean append)
   at System.IO.FileInfo.CreateText()
   at 
Examine.LuceneEngine.SerializableDictionaryExtensions.SaveToDisk[TKey,TValue](SerializableDictionary`2
 sd, FileInfo fi)
   at Examine.LuceneEngine.IndexerExecutive.TimestampLck()
   at Examine.LuceneEngine.IndexerExecutive.get_IsExecutiveMachine()
   at Examine.LuceneEngine.Providers.LuceneIndexer.OptimizeIndex()
   at Examine.LuceneEngine.Providers.LuceneIndexer.Initialize(String 
name, NameValueCollection config)
   at UmbracoExamine.BaseUmbracoIndexer.Initialize(String name, 
NameValueCollection config)
   at UmbracoExamine.UmbracoContentIndexer.Initialize(String name, 
NameValueCollection config)
   at 
System.Web.Configuration.ProvidersHelper.InstantiateProvider(ProviderSettings
 providerSettings, Type providerType)
   --- End of inner exception stack trace ---
   at 
System.Web.Configuration.ProvidersHelper.InstantiateProvider(ProviderSettings
 providerSettings, Type providerType)
   at 
System.Web.Configuration.ProvidersHelper.InstantiateProviders(ProviderSettingsCollection
 configProviders, ProviderCollection providers, Type providerType)
   at Examine.ExamineManager.LoadProviders()
   at Examine.ExamineManager..ctor()
   at Examine.ExamineManager..cctor()
   --- End of inner exception stack trace ---
   at Examine.ExamineManager.get_Instance()
   at UmbracoExamine.UmbracoEventManager..ctor()
   --- End of inner exception stack trace ---
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean 
publicOnly, Boolean noCheck, Boolean& canBeCached, 
RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean 
skipCheckThis, Boolean fillCache)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, 
Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at umbraco.BusinessLogic.Application.RegisterIApplications()
                            

I can get it all working again by deleting all the Examine Indexes and bumping web.config, however this is not a good workable solution as i need to do this every time the site breaks.}

When the index rebuilds, it shows this in the log:

[UmbracoExamine] Field "InternalMemberIndexSet" is listed 
multiple times in the index set "email". Please ensure all names are 
unique
                            

I dont understand what the above is referring to.. my ExamineIndex.config looks like this

<?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 CodePlex: http://umbracoexamine.codeplex.com
-->
<ExamineLuceneIndexSets>
    <!-- The internal index set used by Umbraco back-office - DO NOT REMOVE -->
    <IndexSet SetName="InternalIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/Internal/">
      <IndexAttributeFields>
        <add Name="id" />
        <add Name="nodeName" />
        <add Name="updateDate" />
        <add Name="writerName" />
        <add Name="path" />
        <add Name="nodeTypeAlias" />
        <add Name="parentID" />
      </IndexAttributeFields>
      <IndexUserFields />
      <IncludeNodeTypes/>
      <ExcludeNodeTypes />
    </IndexSet>
  
    <!-- 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>
        <IndexUserFields/>
        <IncludeNodeTypes/>
        <ExcludeNodeTypes />
    </IndexSet>
</ExamineLuceneIndexSets>

Any suggestions as to what might be causing this to break?

Thanks heaps
Greg