What's left? 
Have you done a thorough comparison of the network configuration pages between the 'good' and 'bad' machines? Might turn up something. Firmare version differences? Are there security settings on the network that require the MAC addresses to be authenticated. Devices on the network can and do block unknown devices (MACs).

Have you done a thorough comparison of the network configuration pages between the 'good' and 'bad' machines? Might turn up something. Firmare version differences? Are there security settings on the network that require the MAC addresses to be authenticated. Devices on the network can and do block unknown devices (MACs).
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