Weird error when setting up streaming replication

I'm going through all my usual steps for setting up streaming replication
on a new pair of servers. Modify configs as appropriate, rsync data from
master to slave, etc. I have this all automated with chef, and it has been
pretty bulletproof for awhile. However, today, I ran into this when
starting the slave on this new pair:

* Starting PostgreSQL 9.2 database
server
* The PostgreSQL server failed to start. Please check the log output:
2013-08-08 23:47:30 GMT LOG: database system was interrupted; last known
up at 2013-08-08 23:22:40 GMT
2013-08-08 23:47:30 GMT LOG: entering standby mode
2013-08-08 23:47:30 GMT LOG: WAL file is from different database system
2013-08-08 23:47:30 GMT DETAIL: WAL file database system identifier is
5909892614333033983, pg_control database system identifier is
5909892824786287231.
2013-08-08 23:47:30 GMT LOG: invalid primary checkpoint record
2013-08-08 23:47:30 GMT LOG: invalid secondary checkpoint record
2013-08-08 23:47:30 GMT PANIC: could not locate a valid checkpoint record
2013-08-08 23:47:30 GMT LOG: startup process (PID 10600) was terminated by
signal 6: Aborted
2013-08-08 23:47:30 GMT LOG: aborting startup due to startup process
failure

And I've been stumped. I've completely nuked my data dirs and started over
and gotten the same result, but with different identifier numbers (as I
would expect).

Any Ideas?

Thanks!

QH