I did something stupid today.  I was logged into my slave and thought I was logged into the master.  I altered a table and then realized I was on the wrong server.  So I logged into master and altered the same table.  This created an error when the slave tried to replicate, because the column in the table it was altering already existed.  So the replication could not continue.  I ran this command:

>SHOW SLAVE STATUS \G;

This showed me the error, so I went back and deleted the column on the slave so the alter statement on the slave would finish without error.  Then all you have to do is stop slave and then start slave

>STOP SLAVE;

>START SLAVE;

The slave should catch up to the master shortly.  NOTE TO SELF… make slave user read only.