First of all, I'm not familiar with community server site, although I used ASP.Net Membership extensively.
According to the SO link in your question, the problem is users are missing in cs_Users
table (or might be other table).
1 - You need to find those orphaned rows. Something like this -
SELECT * FROM aspnet_Users WHERE UserId NOT IN (SELECT UserId FROM cs_Users)
2 - Then you either need to delete them or do something.