11
Don't have the lexicon module but:
I think you might be able to get rid of that error/notice by searching your module code for every instance of "XoopsTree" and then replacing it with: XoopsObjectTree.
For example:
$xt = new XoopsTree($this->table, 'topic_id', 'topic_pid');
REPLACE WITH:
$xt = new XoopsObjectTree($this->table, 'topic_id', 'topic_pid');
Now, I don't know if this relates to your difficulty in updating your database table. Sometimes what I do is watch the inline debug MySQL query and if it displays any red errors then it might be because of a poorly constructed db query. Then find the query and FIX it.
Hope that helps!