Master Slave replication broken

[Wilson Mak]

Hi all,

Environment: Dual Master Replication
Only two servers - Master and Slave server (Both can be master)

The master slave replication is broken. I tried to fix with the followings:
STOP SLAVE;
CHANGE MASTER TO master_log_file='mysql-bin-000078', master_log_pos=0;
SLAVE SLAVE;

The query shows no errors. But it can't be fixed. And there is no errors on mysql.err log. The following error logs were created on Feb 2016.

MySQL error logs
=================
160110 4:33:10 [ERROR] Error reading packet from server: Could not find first log file name in binary log index file ( server_errno=1236)
160110 4:33:10 [ERROR] Got fatal error 1236: 'Could not find first log file name in binary log index file' from master when reading data from binary log
160110 4:33:10 [Note] Slave I/O thread exiting, read up to log 'mysql-bin.000077', position 1668
160110 4:40:29 [Note] Error reading relay log event: slave SQL thread was killed
160110 4:44:29 [Note] Slave SQL thread initialized, starting replication in log 'mysql-bin-000077' at position 1669, relay log './DMG-EEServer-Master-relay-bin.000001' position: 4
160110 4:44:29 [Note] Slave I/O thread: connected to master 'repluser@192.168.10.2:3306', replication started in log 'mysql-bin-000077' at position 1669
160110 4:44:29 [ERROR] Error reading packet from server: Could not find first log file name in binary log index file ( server_errno=1236)
160110 4:44:29 [ERROR] Got fatal error 1236: 'Could not find first log file name in binary log index file' from master when reading data from binary log
160110 4:44:29 [Note] Slave I/O thread exiting, read up to log 'mysql-bin-000077', position 1669

relay-log.info
==============
./Master-relay-bin.000001
98
mysql-bin.000078
4
69


5


2
092
2

The directory shown under /var/lib/mysql (Another server)
==================================================================
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000078
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000086
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000084
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000083
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000082
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000081
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000080
-rw-rw---- 1 mysql mysql 117 Jan 7 2016 mysql-bin.000079
-rw-rw---- 1 mysql mysql 1668 Jan 8 2016 mysql-bin.000077

Any clues?

Thanks in advance,
Wilson