User None is disabled. Please contact I got this error from time to time, What is the cause of it

Traceback (most recent call last):
  File "apps/frappe/frappe/app.py", line 99, in application
    init_request(request)
  File "apps/frappe/frappe/app.py", line 195, in init_request
    frappe.local.http_request = HTTPRequest()
  File "apps/frappe/frappe/auth.py", line 44, in __init__
    self.set_session()
  File "apps/frappe/frappe/auth.py", line 78, in set_session
    frappe.local.login_manager = LoginManager()
  File "apps/frappe/frappe/auth.py", line 120, in __init__
    self.make_session(resume=True)
  File "apps/frappe/frappe/auth.py", line 215, in make_session
    frappe.local.session_obj = Session(
  File "apps/frappe/frappe/sessions.py", line 230, in __init__
    self.resume()
  File "apps/frappe/frappe/sessions.py", line 313, in resume
    self.validate_user()
  File "apps/frappe/frappe/sessions.py", line 239, in validate_user
    frappe.throw(
  File "apps/frappe/frappe/__init__.py", line 603, in throw
    msgprint(
  File "apps/frappe/frappe/__init__.py", line 568, in msgprint
    _raise_exception()
  File "apps/frappe/frappe/__init__.py", line 519, in _raise_exception
    raise exc
frappe.exceptions.ValidationError: User None is disabled. Please contact your System Manager.