A couple of problems you might run into...
Firstly, if you are using Windows, it can be a pain actually creating a file named .htaccess, as Windows doesn't seem to like files with an extension only. I usually create the file as htaccess.txt and rename it after uploading to my server.
Secondly, remember that .htaccess is a 'hidden' file, and will not be shown in your FTP client unless the client is configured to show hidden files.
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