If you are using Lucene's trunk (to be 4.0) builds, read on... I just committed LUCENE-2872, which is a hard break on the index file format.
If you are living on Lucene's trunk then you have to remove any previously created indices and re-index, after updating. The change cuts over to a faster on-disk terms dictionary format, which block-encodes term data & metadata between indexed terms. Mike
