EPiFind Indexing error

Hi 

When I ran find index on my commerce site, I received the following error, I have already spent a few hours, but still couldn't figure out what caused this. 

WARN EPiServer.Find.Cms.ContentIndexer: XXXXX-6JMQF72: An exception occurred during reindex operation. System.AggregateException: One or more errors occurred. ---> System.FormatException: Input string was not in a correct format.
   at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.Format(String format, Object[] args)
   at EPiServer.Find.Cms.ContentIndexer.IndexBatch(IEnumerable`1 content, Action`1 statusAction, Int32& numberOfContentErrors, Int32& numberOfBatchErrors, Int32& indexingCount)
   at EPiServer.Find.Cms.ContentIndexer.IndexBatch(IEnumerable`1 content, Action`1 statusAction, Int32& numberOfContentErrors, Int32& numberOfBatchErrors, Int32& indexingCount)
   at EPiServer.Find.Cms.ContentIndexer.<>c__DisplayClass12.<ReIndex>b__9(IEnumerable`1 currentBatch, ParallelLoopState loopstate)
   at System.Threading.Tasks.Parallel.<>c__DisplayClass42_0`2.<PartitionerForEachWorker>b__1()
   at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask)
   at System.Threading.Tasks.Task.<>c__DisplayClass176_0.<ExecuteSelfReplicating>b__0(Object )
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
   at System.Threading.Tasks.Parallel.PartitionerForEachWorker[TSource,TLocal](Partitioner`1 source, ParallelOptions parallelOptions, Action`1 simpleBody, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally)
   at System.Threading.Tasks.Parallel.ForEachWorker[TSource,TLocal](IEnumerable`1 source, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally)
   at System.Threading.Tasks.Parallel.ForEach[TSource](IEnumerable`1 source, ParallelOptions parallelOptions, Action`2 body)
   at EPiServer.Find.Cms.ContentIndexer.ReIndex(Action`1 statusAction, Func`1 isStopped)
---> (Inner Exception #0) System.FormatException: Input string was not in a correct format.
   at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.Format(String format, Object[] args)
   at EPiServer.Find.Cms.ContentIndexer.IndexBatch(IEnumerable`1 content, Action`1 statusAction, Int32& numberOfContentErrors, Int32& numberOfBatchErrors, Int32& indexingCount)
   at EPiServer.Find.Cms.ContentIndexer.IndexBatch(IEnumerable`1 content, Action`1 statusAction, Int32& numberOfContentErrors, Int32& numberOfBatchErrors, Int32& indexingCount)
   at EPiServer.Find.Cms.ContentIndexer.<>c__DisplayClass12.<ReIndex>b__9(IEnumerable`1 currentBatch, ParallelLoopState loopstate)
   at System.Threading.Tasks.Parallel.<>c__DisplayClass42_0`2.<PartitionerForEachWorker>b__1()
   at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask)
   at System.Threading.Tasks.Task.<>c__DisplayClass176_0.<ExecuteSelfReplicating>b__0(Object )<---