In 1.0.4, the journal was not pruning the commit record index when processing deferred frees in an attempt to work around  and only the commit records from "lastDeferredReleaseTime" forward were processed.
When the journal is then opened under 1.0.6, all historical commit records are considered (the start time is 0L). This causes the RWStore to consider commit records whose deferred frees have already been release, which is the root cause of the thrown exception.
Martyn is working on a migration utility which will simply prune the commit record index, removing all entries up to the "lastDeferredReleaseTime". This utility could then be applied to a 1.0.4 journal to make it compatible with 1.0.6.
 http://sourceforge.net/apps/trac/bigdata/ticket/440 (BTree can not be cast to Name2Addr)