This issue has occurred repeatedly since we've upgraded to version 5.0 and began using LDAP integration. It happens at least once every 24 hours.
What occurs is this:
1. A user complains that they can't login (all of our users are now LDAP authenticated).
2. I attempt to login with my LDAP credentials, which also fail.
3. I login as our jiraadmin user (stored in the internal DB), which succeeds.
4. After I do that, everyone can login with LDAP again.
The logs don't provide much information that we can use, not sure what is causing this or what we can modify to stop it.