Files / Folders Permissions
For security reasons, the permissions on the folders/directories in your hosting account should NOT be 777 which may cause the message "500 internal server error".
The same rule applies to the files, ie the contents of that folder and they should not be "world writable" (777 permissions).
The recommended settings in relation to the upper permissions are 755 for folders/directories and 644 for files to be adequately protected.