How to solve TinyMce image manager Network Error
If you're using .htaccess it may be possible you're heading to a CI controller rather than the file you're looking for.
Here is an example mod_rewrite rule that might help. Often it's worth checking your access log to see which file is being called also.
RewriteEngine onRewriteCond $1 !^(index\.php|assets|media|favicon\.ico|ipadicon\.jpg|tiny_mce)RewriteRule ^(.*)$ /index.php/$1