Thread:Extension talk:Lucene-search/Internal error in SearchEngine trying to make WikiSearcher: null

I'm encountering a strange error msg today. It's working fine before, it started just after I restarted the server.

Following is the log from the server. [pool-2-thread-13] ERROR org.wikimedia.lsearch.search.SearchEngine - Internal error in SearchEngine trying to make WikiSearcher: null

On Browser I got: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  Error: 500 Server error 500 Server error Internal error in SearchEngine: null LSearch daemon on localhost

I'll really appreciate if you can help me to understand the error. Thanks in advance,

sincerely yours Babur