only ONE missing admin icon, not ALL

Hey everyone. See the screenshot of my problem here. As you can see, I only have one missing icon. But from my sleuthing of the wp-admin backend, all of the admin button icons are contained in one file, not individual files. The file is located here:
~/wp-admin/images/icons32.png

I checked out these other similar posts, but these didn’t quite match up with my problem:

• here
• here
• here

My icons32 isn’t corrupt. The entire PNG can be viewed directly from my server with no errors here.

There doesn’t seem to be any problems in my .htaccess file:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Any ideas?