My MySQL Slave server has stopped replicating its' Master

I have a backup server that replicates my production server's mysql database, awhile ago I setup a staging server with the same php script with the only difference being that I gave it a read only mysql user so it can't make changes to the database, and only read from it. I'm not sure if it had anything to do with this but today I saw the backup had stopped working and it has the following error:

Got fatal error 1236 from master when reading data from binary log: 'Client requested master to start replication from impossible position'

Here is the output from the maser:

  File: mysql-bin.000208
        Position: 24383202
    Binlog_Do_DB: sexxymofo
Binlog_Ignore_DB:

and the slave:

Slave_IO_State:
                  Master_Host: 184.168.76.5
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000193
          Read_Master_Log_Pos: 54442531
               Relay_Log_File: mysqld-relay-bin.000155
                Relay_Log_Pos: 54442676
        Relay_Master_Log_File: mysql-bin.000193
             Slave_IO_Running: No
            Slave_SQL_Running: Yes
              Replicate_Do_DB: sexxymofo
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 54442531
              Relay_Log_Space: 54442875
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 1236
                Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'Client requested master to start replication from impossible position'
               Last_SQL_Errno: 0
               Last_SQL_Error:

as you can see the slave has got ahead of the master and into a non-existent position, can anyone help? I'm probably gonna restart the process but I would like to make sure it doesn't happen again.

Solution

Position is position within the file so the slave is way behind, on file mysql-bin.000193, and the master is already on mysql-bin.000208.

The impossible about this setup might be that the master has purged the file mysql-bin.000193 and since the slave isn't running IO that file hasn't been transferred.