If you are on a corporate network, there's a good chance you connect to the Internet using a proxy server. Dropbox works just fine through HTTP(S) proxy servers.
Show instructions for:
If Dropbox is still having trouble connecting and you don't know if you use a proxy server or not, try selecting No proxy.
The proxy settings you add using these steps aren't used to update the Dropbox app. Dropbox uses your OS network settings to apply