crypt_r() issue when viewing HTTP auth page

When viewing a page that is HTTP auth password protected, we sometimes get an error 500 (internal server error), but 100% of the time, a browser reload of the page makes it work the second time around. The ngnix error log shows this:

2012/12/19 15:50:43 [crit] 28799#0: *6224 crypt_r() failed (2: No such file or directory), client: 108.199.xxx.xxx, server: dev.digitalpoint.com, request: "GET /admin.php HTTP/1.1", host: "dev.digitalpoint.com", referrer: "http://dev.digitalpoint.com/"

It makes me wonder if maybe nginx worker processes can never read the auth_basic_user_file the first time it tries for some reason (but always can after that first try)? Like I mentioned, it will work properly 100% of the time on a browser reload.

relevant part of nginx conf:

location /admin.php {
auth_basic Restricted;
auth_basic_user_file /etc/nginx/.passwd;
<...clipped...>
}

/etc/nginx/.passwd exists and I assume everything is okay with it since everything works as expected on browser reload.

Anyone know how to fix this?