Backslashes should be URI-escaped in URI paths, so you'll need to account for this in your rewrite condition:
Code:
RewriteCond %{REQUEST_URI} ^(.*)(\\|%5C)(.*)$
RewriteRule .* %1/%3 [R=301,NC,L]
However, using Apache to change backlashes to forward slashes is inefficient as it will only change one character per request, resulting in one extra requests per backslash in the URL path for each resource. Even though you don't have access to the source for the flash movie, you can try a hex editor, flash decompiler or SWF editor to change the resource. Failing that, pipe any URI paths through a script to generate the 301 redirect:
Code:
RewriteCond %{REQUEST_URI} (\\|%5C)
RewriteRule (.*) fixslashes.php?uri=$1 [L]
fixslashes.php:
PHP Code:
<?php
/* The "uri" query param is unnecessary, but using it is less magical & mysterious */
if (isset($_REQUEST['uri'])) {
$path = $_REQUEST['uri'];
} else {
$path = $_SERVER['REQUEST_URI'];
}
$path = preg_replace('/\\+|%5C/', '/', $path);
header('Location: ' . $path, True, 302);
A rewrite map would be useful here, but you can't define external rewriting programs in .htaccess.