Bad version number in .class file

I have setup dbsight on Debian with Tomcat5, and java-1.5.0-sun jdk. Have created index 'bol', initial query etc ok. Now trying to recreate this index but getting the following. Where next please ?

INFO 2007-10-15 12:27:14,382- ~~~~~~~ bol:unlockStoppedIndex ...
INFO 2007-10-15 12:27:14,383- unlock temp files if exists
INFO 2007-10-15 12:27:14,385- ~~~~~~~ bol:maybeBuildSynonyms ...
INFO 2007-10-15 12:27:14,399- ~~~~~~~ bol:reCreateIndex ...
INFO 2007-10-15 12:27:14,405- buiding index for bol
INFO 2007-10-15 12:27:14,414- Period Table:
INFO 2007-10-15 12:27:14,417- TaskScheduler provider class is 'class net.javacoding.xsearch.core.super.new.B'
INFO 2007-10-15 12:27:14,449- DBCP using driver: com.mysql.jdbc.Driver at URL: jdbc:mysql://localhost:3306/bol
ERROR 2007-10-15 12:27:15,765- When reCreateIndex:java.lang.UnsupportedClassVersionError: Bad version number in .class file
WARN 2007-10-15 12:27:15,768- stopping indexing