ArcEarth 1.4 does not appear to support NTLM proxy authentication, which is an issue which we encountered with previous versions as well. After launching AE on a computer with correctly configured system level internet options, two error messages appear:
"Failed to use proxy: the credentials are invalid Unable to connect to the remote server"
"The Remote server returned an error (407) Proxy Authentication Required"
Manually configuring the correct proxy server (using IP or hostname), username (with and without domain suffix) and password results in the same errors. Overwriting the config.xml file in the AppData/Roaming folder or the Program Files/ArcGIS/Earth/Bin folders does not change the outcome.
The sign-on window for ArcGIS online loads and is able to navigate the proxy, but it appears to use Internet Explorer so that's not surprising. ArcEarth itself does not login, displaying the two errors listed above after "Sign In" is clicked.
ESRI tech support referred us to this forum for assistance, we'd love to get this application working in our organization.