JRuby + Neo4J Problems

I have JRuby on Rails app, which is using an ueber JAR to access Neo4J. The Neo4J database is in the rails root directory unter “data/”. By starting the HTTP Server I got today this Exception:

IllegalArgumentException: No index provider 'lucene' found. Maybe the intended provider (or one more of its dependencies) aren't on the classpath or it failed to load.

The problem was in the “data/”. In some way it was corrupt. I am not sure. After I exchanged the “data/” directory with an older version, the HTTP Server started without any problems.