How did you set up the standby? Did you initialize it from an offline backup of the master's data directory, perhaps? The log shows that the startup took the the "crash recovery first, then start archive recovery" path, because there was no backup label file. In that mode, the standby assumes that the system is consistent after replaying all the WAL in pg_xlog, which is correct if you initialize from an offline backup or atomic filesystem snapshot, for example. But "WAL contains references to invalid pages" could also be a symptom of an inconsistent base backup, cause by incorrect backup procedure. In particular, I have to ask because I've seen it before: you didn't delete backup_label from the backup, did you?
Well, I cannot answer this right now, but makes all sense and is possible.
I've just confirmed. That was indeed the case, the script was removing the backup_label. I've just removed this line and synced it again, it is running nice (for past 1 hour at least).
Thank you guys for all your help, and sorry for all the confusion I caused.
Best regards,
-- Matheus de Oliveira Analista de Banco de Dados Dextra Sistemas - MPS.Br nível F! www.dextra.com.br/postgres