rewrite rule 404 not found

why in the bandidos wont this work? 404 not found

RewriteRule ^threads/cats/([0-9]+)$ /forum/cats.php?id=$1

apache error log:

[Thu Jan 20 20:18:18 2011] [error] [client 127.0开发者_开发技巧.0.1] File does not exist: C:/wamp/www/threads
[Thu Jan 20 20:18:18 2011] [error] [client 127.0.0.1] File does not exist: C:/wamp/www/favicon.ico

Try prefixing it with a / and add an ? just incase it's not necessary.

RewriteRule ^/?threads/cats/([0-9]+)$ /forum/cats.php?id=$1