I'm having a similar problem. Clean install of 2.2.6 on shared hosting - can't unpack locally so I have had to FTP up the whole lot (I've tried several times, and also 2.2.5). To begin with I wasn't seeing anything working in the manager that involved a right hand leaf/pane (ie it showed the tree, but nothing if you clicked on a menu item, or tried to edit a resource).
To get round that I modified compress_css and compress_js in the database. Result - can now access all the manager.
However - when I go to Package Manager or Try to edit a resource, I now get a popup error:
Unexpected token '<': Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
etc
I can't check if the host is running mod_security, as per install RTFM - but is that the issue? When I go to edit a resource for example, there is only one response error in the list, and it's for
POST /connectors/element/template.php
This is the POST
id=1&action=getList&combo=1&limit=0&HTTP_MODAUTH=modx50c107e52e7904.85594071_150c10a9fc88355.38404051]
Similarly, on the Package Manager, there are a number of requests that complete successfully, except for
POST /connectors/workspace/packages-rest.php
This is the POST
action=getList&provider=1&HTTP_MODAUTH=modx50c107e52e7904.85594071_150c10a9fc88355.38404051
It doesn't seem to happen for editing Files, Templates or other instances of action=getList (albeit in different files). It seems to be on those two specific actions. What can I do to fix?