I have searched. Gods only know how I have searched. I cannot find a straight answer to this, or really, any answer. I am upgrading from the latest version of D6 as of 8-21-14 to the latest version of D7. When I followed the recommended upgrade method, I got such a dog's breakfast of missing user pictures, munged blog posts and bloody taxonomy upgrade debris that I started over with all the modules enabled, as others who've faced those problems recommended.
Well, now I can't get past system update 7053, and nothing I have found can give me any indication of why, not even digging through the database itself, the code or the logs. I don't know what table has the duplicate key referenced in the error in the subject, which, again, is:
SQLSTATE: Integrity constraint violation: 1062 Duplicate entry 'user-menu' for key 'PRIMARY' [error]
Performed update: system_update_7053
Such is what drush returns, giving me no idea of where the duplicate entry is. I've looked through the menu tables, thinking perhaps this is the problem, but no. Nor is it in the system or variable tables. Or blocks. Yes, I've cleared caches for what that's worth.
I never post here unless I'm at my wit's end, and I'm kind of there. Thank you.