Since selective sync works on your work computer, but not on your home one, it appears the issue can be isolated to your home computer. Sometimes third party software (like security software) can route your computer’s traffic through a software proxy, in order to analyze it, which could explain this behaviour. Here are the steps to check if a proxy is in place:
1. On your Mac, go to System Preferences then go to Network. The network settings window will appear.
2. If you are connected to your home network via Wi-Fi, select Wi-Fi from the list on the left, then click the Advanced... button on the right.
3. In the window that appears, click the Proxies tab from the top part of the window.
4. On the Proxies tab, in the list of protocols displayed under the "Select a protocol to configure" heading, see if any of them have a checkmark next to them.
6. If any of the protocols are checked, try unchecking them, then quit Dropbox app from the menu icon, wait for it to stop, start it again and see if the selective sync settings still show that error message.
Hope this helps,
Razvan
