Active Directory encountered a checksum error reading from the database. This may be a transient problem accessing the database and diagnostics should be run against it. However if this error persists, you may need to restore the database from a backup.
A possible reason for this error is database corruption. See the Technet articles under Links on how to run database diagnostics and how to recover from database corruption.
For more information, see:
Active Directory Backup and Restore
Database Issues