rewrite problem [member profile pages]

I want to set up a member profile page for each member on my site
eg user joe would have a profile at /members/joe

I have created a page “members” and assigned it a page template
the template uses a username parameter

so mysite.com/members?username=joe should receive the parameter “joe”

I have the following Rewite rule in .htaccess:

RewriteRule ^members/([a-zA-Z0-9_-]+)$ /members?username=$1
RewriteRule ^members/([a-zA-Z0-9_-]+)/$ /members?username=$1

I have registered the query var 'username' via functions.php

add_filter(‘query_vars’, ‘add_my_var’);

function add_my_var($public_query_vars) {
$public_query_vars[] = ‘username’;
return $public_query_vars;
}
`

When i go to mysite.com/members/123 it works as expected (it behaves as if I had visitied mysite.com/membersmembers?username=123) and it will print out “profile for member with username 123” – so the parameter seems to be getting passed Okay.

however, when i visit mysite.com/members/joe (or any other URI with characters instead of numbers) – I get a 404 page not found.

Any ideas what’s going on ?