You are unable to log into an Acquia-hosted site through Dev Desktop due to the error:
"Login failed. Network error: Couldn't connect to server."
The error message typically means Dev Desktop is failing to communicate with the internet, so there may be network restrictions. To rule out a local network issue, try to connect from your home or tether off of your cell phone. You may need to contact your local network administrator to add an exception to the network.