Try this:
Options +FollowSymlinks
RewriteEngine on
RewriteCond %{REQUEST_URI}!/maintanence.html$
RewriteRule $ /maintenance.html [R=307,L]
Also, instead of creating the file locally and pushing it to the server, do you have cPanel access or something to your server where you can create a new file, name it .htaccess and put all of this in it from your web-control panel and not via FTP?