if it’s not a .htaccess problem there’s also a setting which redirects a manager user: "Security" -> "Manager Users" -> "nameofthemanageruser" -> "User"-tab -> the field "Manager Login Startup" (is used to select a frontend page, to which a manager user will be redirected to after logging in)
My first guess is that the trouble started when you turned Friendly URLs on and renamed .htaccess but you didn’t notice it at first because of the MODx cache and maybe your browser cache.
Try the suggestions in the previous messages (clearing the MODx cache and your browser cache after each one!). I would recommend using IE7 or Safari for this because Firefox is not reliable about clearing its cache. While FURLS are on, make sure there is a .htaccess file (not ht.access) in the /manager folder that turns the rewrite engine off for that folder.
Try doing an upgrade install (but be sure *not* to intall any sample content or add-ons). That won’t touch your content. Clear the caches again and check.
If those ideas don’t help, turn friendly URLs off and rename .htaccess to ht.access (in the root and manager folders). If that solves the problem, it’s definitely a problem with the rewrite rules in the .htaccess file in the MODx root (where assets, frames, include, manager, etc. are).
If things are still messed up, there’s a chance that one or more files were corrupted in your FTP upload.
