Error no device found when loading overlay

I have the same problem.

I logged in via SSH to my PYNQ-ZU board. Then ran

sudo -s 
source /etc/profile.d/ 

In Python prompt, I ran some lines of code and get the following error:

>>> from pynq.overlays.base import BaseOverlay
>>> from import *
>>> base = BaseOverlay("base.bit")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/xilinx/pynq/overlays/base/", line 48, in __init__
    super().__init__(*args, **kwargs)
  File "/home/xilinx/pynq/", line 336, in __init__
    super().__init__(bitfile_name, dtbo, partial=False, device=device)
  File "/home/xilinx/pynq/", line 111, in __init__
    device = Device.active_device
  File "/home/xilinx/pynq/pl_server/", line 94, in active_device
    raise RuntimeError("No Devices Found")
RuntimeError: No Devices Found