The navigation changes a bit in 4.2.1
See
Login Required - vBulletin JIRA
and
Login Required - vBulletin JIRA
These fix the navigation table URLs, do this before you upgrade after you have backed up.
Code:
Content visible to verified customers only.
Full 4.2.1 changes...
[4.2.1 by Votes] Issue Navigator - vBulletin JIRA