Unable to change user name

Hi all, i added one user name wrongly then i try to change that name but it not changed,
then i try to change that user name by using backend, name was changed but
that user getting error when he try to login

Traceback (most recent call last):
File “apps/frappe/frappe/www/app.py”, line 27, in get_context
boot = frappe.sessions.get()
File “apps/frappe/frappe/sessions.py”, line 143, in get
bootinfo = get_bootinfo()
File “apps/frappe/frappe/boot.py”, line 72, in get_bootinfo
bootinfo.notification_settings = get_notification_settings()
File “apps/frappe/frappe/boot.py”, line 393, in get_notification_settings
return frappe.get_cached_doc(“Notification Settings”, frappe.session.user)
File “apps/frappe/frappe/init.py”, line 1144, in get_cached_doc
doc = get_doc(*args, **kwargs)
File “apps/frappe/frappe/init.py”, line 1272, in get_doc
doc = frappe.model.document.get_doc(*args, **kwargs)
File “apps/frappe/frappe/model/document.py”, line 82, in get_doc
return controller(*args, **kwargs)
File “apps/frappe/frappe/model/document.py”, line 123, in init
File “apps/frappe/frappe/model/document.py”, line 169, in load_from_db
File “apps/frappe/frappe/init.py”, line 577, in throw
File “apps/frappe/frappe/init.py”, line 549, in msgprint
File “apps/frappe/frappe/init.py”, line 500, in _raise_exception
raise exc
frappe.exceptions.DoesNotExistError: Notification Settings “abc@gmail.com” not found

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File “apps/frappe/frappe/website/serve.py”, line 18, in get_response
response = renderer_instance.render()
File “apps/frappe/frappe/website/page_renderers/template_page.py”, line 84, in render
html = self.get_html()
File “apps/frappe/frappe/website/utils.py”, line 524, in cache_html_decorator
html = func(*args, **kwargs)
File “apps/frappe/frappe/website/page_renderers/template_page.py”, line 95, in get_html
File “apps/frappe/frappe/website/page_renderers/template_page.py”, line 162, in update_context
data = self.run_pymodule_method(“get_context”)
File “apps/frappe/frappe/website/page_renderers/template_page.py”, line 224, in run_pymodule_method
return method(self.context)
File “apps/frappe/frappe/www/app.py”, line 29, in get_context
raise frappe.SessionBootFailed from e