It’s probably the server config as this seems to be a distinct though not mainstream problem according to this forum.
For my clients I’ve had to look for another CMS (Website Baker as a poor compromise). They were not interested in moving to another hosting company at this point.
The issue is not unique to the latest MODx rev as the host’s site also broke a site where MODx v 4.5 was working fine previously. This coincided with that company’s (AussieHQ) move to MySQL 5 and PHP 5. My feeling is that one of their defaults for PHP 5, in particular, is breaking some of the include commands in MODx’s manager module (any recent version).
If we could work out what defaults break the manager module in particular, then we can fix it by requesting a change to that configuration.
For now, I insist that my clients hosting company ensures thay can run MODx manager without any issues.
Some companies in Australia actually offer MODx as part of their hosting package.
FWIW - some php/mysql heroes can check a dump of the hosting environment that seems to break the manager module at
http://edutainment.com.au/phpinfo.php
If we could locate the consistent server deal breaker in the configuration, we could revise the installation script to include new alerts (as it does with ensuring certain folders and files are writeable) before running the full install in the next rev.