All logins blocked

Problem/Motivation

I have inherited a site with login security. It has been fine for a few weeks, but today it blocked access to every account. The only way I could regain access was to edit the DB: system -> sites/all/modules/contrib/login_security/login_security.module set status = 0, then truncate the cache tables.

Once logged in, enabled the login security module, and tried to login in through an incognito browser session, but was once again denied access until the module was disabled.

I tried clearing both the flood and login_security_track tables then enabling the module, but had the same results.

The same user name and password was used in each attempt.

Any ideas on what may cause this?