CB Tools: Users database warning

Hello CB experts,

I'm finalizing our CB user database (approx. 830 users) and ran a DB check using the CB tools from within the Joomla interface. Lots and lots of red scary print:

Warning: 12929 entries in the core_acl_aro table without corresponding users table rows.

After backing up, I clicked the provided link to fix the errors, but they persist. I've been searching these forums (and the Joomla forums) for some guidance, and the closest I found to the problem was this answer from nant:

www.joomlapolis.com/forum/146-general/206742-check-user-database-issue#206761

But I'm not dealing with a migration from one version of Joomla to another, unlike the OP. Also, this thread mentioned a similar error:

www.joomlapolis.com/forum/153-professional-member-support/204425-solved-no-users?limitstart=0

but I'm not losing users after the fix. The fix doesn't appear to be doing anything (or able to do anything, in my case).

I am able to do everything else in CB - edit users, add fields, etc. But this error worries me. Should I be worried? Could CB be having a conflict with another plugin?

Thank you for your help!
CB 1.9
CBJuice2
Joomla 2.5.9