On IBM JDK there is problem with HashMap.findNonNullKeyEntry when you try to access to elements in map from several threads.
Related issue

java.util.HashMap.findNonNullKeyEntry(HashMap.java:601)
java.util.HashMap.getEntry(HashMap.java:585)
java.util.HashMap.get(HashMap.java:571)
org.hibernate.jdbc.ColumnNameCache.getIndexForColumnName(ColumnNameCache.java:23)
org.hibernate.jdbc.ResultSetWrapper.findColumn(ResultSetWrapper.java:61)
org.hibernate.jdbc.ResultSetWrapper.getLong(ResultSetWrapper.java:185)

Map ColumnNameCache.columnNameToIndexCache should be synchronized.

this.columnNameToIndexCache = Collections.synchronizedMap(new HashMap( columnCount ));