The navigation changes a bit in 4.2.1
See http://tracker.vbulletin.com/browse/VBIV-15312
and http://tracker.vbulletin.com/browse/VBIV-15023
These fix the navigation table URLs, do this before you upgrade after you have backed up.
Code:
UPDATE `navigation` SET `url` = REPLACE(`url`,'{options','{vboptions') WHERE `fromusername` LIKE '%{options%';
UPDATE `navigation` SET `url` = REPLACE(`url`,'{userinfo','{bbuserinfo') WHERE `fromusername` LIKE '%{userinfo%';
Full 4.2.1 changes... http://tracker.vbulletin.com/secure/...equestId=11035
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