Getting a Parse Error in Manager

Today I started getting error messages from my ModX Evo installation. When I logged in to Manager I saw the follow error:

Warning: Cannot modify header information - headers already sent by (output started at /home/saintmon/public_html/manager/includes/header.inc.php:12) in /home/saintmon/public_html/manager/includes/document.parser.class.inc.php on line 3647
« MODX Parse Error »
MODX encountered the following error while attempting to parse the requested resource:
« PHP Parse Error »
PHP error debug
Error : include_once() [function.include]: Failed opening '/home/saintmon/public_html/assets/plugins/managermanager/widgets/mm_renamefield/mm_renamefield.php' for inclusion (include_path='.:/usr/lib/php:/usr/local/lib/php:/home/saintmon/public_html/manager/includes/')

Warning: include_once(/home/saintmon/public_html/assets/plugins/managermanager/widgets/mm_renamefield/mm_renamefield.php) [function.include-once]: failed to open stream: Permission denied in /home/saintmon/public_html/assets/plugins/managermanager/mm.inc.php on line 61

Warning: include_once() [function.include]: Failed opening '/home/saintmon/public_html/assets/plugins/managermanager/widgets/mm_renamefield/mm_renamefield.php' for inclusion (include_path='.:/usr/lib/php:/usr/local/lib/php:/home/saintmon/public_html/manager/includes/') in /home/saintmon/public_html/assets/plugins/managermanager/mm.inc.php on line 61
ErrorType[num] : WARNING[2]
File : /home/saintmon/public_html/assets/plugins/managermanager/mm.inc.php
Line : 61
Source : Plugin
Basic info
REQUEST_URI : http://www.saintmonicaconverse.net/manager/index.php?a=27&id=1
Manager action : 27 - Editing resource
Current Plugin : ManagerManager(OnDocFormPrerender)
Referer : http://www.saintmonicaconverse.net/manager/index.php?a=1&f=tree
User Agent : Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0
IP : 173.174.230.17
Benchmarks
MySQL : 0.0031 s (6 Requests)
PHP : 0.0223 s
Total : 0.0254 s
Memory : 1.14972686768 mb

Backtrace
1 include_once()
manager/index.php on line 288
2 DocumentParser->invokeEvent()
manager/actions/mutate_content.dynamic.php on line 492
3 DocumentParser->evalPlugin()
manager/includes/document.parser.class.inc.php on line 3379

This just started today. The install has been working fine for more than a year.

Files can get corrupted. Check that the file it's trying to include is in that location (/home/saintmon/public_html/assets/plugins/managermanager/widgets/mm_renamefield/mm_renamefield.php) and check that it's OK, has the right permissions and is readable.

The other messages about headers is only because PHP is setting its own headers to display its own errors, and MODX is also trying to set its own headers. Ignore them.

One other possibility. One time long ago I ran across a similar situation when the hosting provider configured a security setting that would not allow the including of PHP files deeper than four levels. Once they changed that to six levels then my scripts (actually it was TinyMCE) could run. So "assets/plugins/managermanager/widgets/mm_renamefield/" would have been too many levels in that case.