Fixing a 500 Error on the Manager Login While the Site Still Works

A manager-only 500 error after migration usually means the public site and the manager have diverged in file availability, include paths, or hosting behavior.

Donor Error Pattern

Warning: require_once(.../manager/includes/sniff/phpSniff.class.php): failed to open stream
Fatal error: require_once(): Failed opening required .../phpSniff.class.php in browsercheck.inc.php

What to Check First

• Whether the referenced manager file really exists on the target host and has the same case-sensitive name.
• Whether the migration copied the complete manager include tree.
• Whether include paths or open_basedir-style restrictions differ between hosts.
• Whether the file exists locally but failed to upload cleanly in binary or text mode.

Because the front-end still worked, this donor case was never about the full project being broken. It was a scoped manager dependency issue, which is exactly the kind of failure that should be isolated quickly before bigger changes are attempted.