To answer Coffee Administrator's question about the AirDroid versions, they are all running the same version:
MacBook Pro 2014: Running AirDroid Desktop Client 3.0.1.dmg (login works)
Samsung Galaxy Note 10.1 Tablet: AirDroid Version 3.0.1 (login does NOT work)
Samsung Galaxy Note 3 Phone: AirDroid Version 3.0.1 (login does NOT work)
On the MacBook, I can authenticate with no problem; however, on the tablet/phone, the same error appears with a "Failed to sign in, please retry. (-11111)". I am able to connect (and send messages, see files/applications, and make phone calls) between all three devices "if" I bring up Safari and enter the corresponding network URL for the device (i.e. 192.168.1.x:8888) when all are attached to the same Wi-Fi network, but being that I'm unable to actually "login" to the site, I'm unable to take advantage of certain functions that "logging in" would provide.
Hope this clarifies.
Richard