Build a new slave from existing slave on older version (2 replies)

New here, and need some help.

My current setup has a Primary DB running 5.0.95, with a slave (Slave #1) on the same version. I want to build a second slave (Slave #2) running 5.1.69.

In my first attempt, I simply stopped Slave #1, and copied all the data files to Slave #2, changed the server ID, and fired it up. That worked fine. For 30 minutes. Then I got the following error, and slave #2 shut down.

131109 17:11:12 [ERROR] /usr/libexec/mysqld: Incorrect key file for table './vb/post.MYI'; try to repair it
131109 17:11:12 [ERROR] /usr/libexec/mysqld: Incorrect key file for table './vb/post.MYI'; try to repair it
131109 17:11:12 [ERROR] Slave SQL: Error 'Incorrect key file for table './vb/post.MYI'; try to repair it' on query. Default database: 'vb'. Query: '...(truncated for readability)'
131109 17:11:12 [Warning] Slave: Incorrect key file for table './vb/post.MYI'; try to repair it Error_code: 126
131109 17:11:12 [Warning] Slave: Incorrect key file for table './vb/post.MYI'; try to repair it Error_code: 126
131109 17:11:12 [Warning] Slave: Incorrect key file for table 'post'; try to repair it Error_code: 1034
131109 17:11:12 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.000237' position 32044250


I tried rebuilding Slave #2 3 times with the same result every time. I suspect the problem is that I built Slave #2 by copying data files, and since the version is different, that doesn't work. I suspect I need to build Slave #2 from a mysqldump.

First question: Am I correct in my assumption as to why it fails?
Second question: How would I build Slave #2 from a mysqldump off Slave #1 without stopping the master?

Thanks in advance for any help.