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Not sure how your server is configured but mine is set up so that subdomain.mydomain.com is a subdirectory like this:

http://www.mydomain.com/subdomain/

in robots.txt you would simply need to put

User-agent: *
Disallow: /subdomain/

Others may have a better way though.

HTH

Steve

Different computers on the same network / IP segment not loading the site could be a Proxy server OR DNS Setting.

I'm on Mac so that's what I know about.

What are your Mac network settings?

Do you get an IP address?

Can you load other websites from the same virtual hosting server?

Can you load the website via the IP address?

Whats the URL of the website?

Steve