Exception in production

[Max Metral]

I'm getting this exception, any thoughts?

 

MESSAGE: Object reference not set to an instance of an object.

 

SOURCE: Lucene.Net

 

Server stack trace: 

   at Lucene.Net.Store.FSIndexInput.ReadInternal(Byte[] b, Int32 offset,
Int32 len)

   at Lucene.Net.Store.BufferedIndexInput.ReadBytes(Byte[] b, Int32
offset, Int32 len)

   at
Lucene.Net.Index.CompoundFileReader.CSIndexInput.ReadInternal(Byte[] b,
Int32 offset, Int32 len)

   at Lucene.Net.Store.BufferedIndexInput.Refill()

   at Lucene.Net.Store.BufferedIndexInput.ReadByte()

   at Lucene.Net.Store.IndexInput.ReadInt()

   at Lucene.Net.Store.IndexInput.ReadLong()

   at Lucene.Net.Index.FieldsReader.Doc(Int32 n)

   at Lucene.Net.Index.SegmentReader.Document(Int32 n)

   at Lucene.Net.Index.MultiReader.Document(Int32 n)

   at Lucene.Net.Search.IndexSearcher.Doc(Int32 i)

   at Lucene.Net.Search.Hits.Doc(Int32 n)

                (my frames above this)