SAMSUNG | Unable to establish ADB connection

The problem is:

===Rooting by recovery image based root method...===
Switching to download mode.
Waiting for modem. a00000Do not disconnect the phone!
Connecting.
Reading PIT.
Sending recovery image. This will take a while.
Switching to normal mode.
Waiting for modem. a00000Do not disconnect the phone!
Establish ADB connection. a00000Do not disconnect the phone!
E: Unable to establish ADB connection.
Error for server: Unable to establish ADB connection.

Solution:

Check the Always allow from this computer checkbox when you attact the usb cable