If you get -21000 error code on AirDroid Windows/Mac,
1. Please use IE browser (IE for Windows users, and Safari for Mac users) to open the following link:
http://push.airdroid.com:8098/session/get
The result should be something like this: {"data":{"data":"b8aa1abc89c624e3b3af"},"ret":0}
2. If you can open the link normally, then you need to try to sign in again. If you still encounter sign in failure all the time, you have to check if AirDroid is blocked by your firewall. If you turn off your firewall, and you still cannot sign in, please leave your comment and let us know.
If you cannot open the link properly, first, you need to check if your IE browser is using proxy or not. Turn off your proxy, and try to sign in again. Second, if you are using VPN, turn off your VPN and try to sign in again.
If you have 404, 500, or 502 error codes opening above link, please leave a comment attach your logs.
How to find AirDroid logs?
Windows: C:\Program Files\AirDroid\Exception
Mac: Click Finder--Click Go--Press Alt until Library shows--Click Library
More details of other error codes: http://forum.airdroid.com/discussion/14 ... red#latest