How-to: Turn on error logging in Magento
Sometimes you need to see errors that aren't otherwise visible (I needed it to analyze Magento - Erply POS sync errors). Here's how to turn on error logging in Magento and read the error logs:
1) Turn on error logging: Admin > Configuration > Developer > Log Settings > Enabled = Yes
2) FTP to open files var/log/system.log and var/log/exception.log and read the last lines for latest errors.