How to repair mysql master-master replication errors

Say you have a server in the replication setup down for a couple of days, and when you turn it back on and check if sync is working proper:

mysql -uroot -p
show slave status\G

In case it's all good:

Slave_IO_Running: Yes
Slave_SQL_Running: Yes

Possible error 1:

Slave_IO_Running: Yes
Slave_SQL_Running: No

Can be fixed by this url