Hi,
Just tested with my TRB140 running on firmware version TRB1_R_00.02.03.2 and was able to get gateway's status with authorization by admin password.
Is authorization by serial number also not working for you or the issue only present with admin password?
To begin with, if you did not change much of device's configuration, try resetting device to factory defaults by holding reset button for 12s and check whether you're able to get response with admin password authentication.