djangoでアカウント作成機能を追加していますが、エラーを解決できません。
カスタムユーザーを使用しています。
ネットの情報を参考にしています。
わかるかたお願いします。

Internal Server Error: /accounts/signup/
Traceback (most recent call last):
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/views/generic/base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/views/generic/base.py", line 97, in dispatch
    return handler(request, *args, **kwargs)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/views/generic/edit.py", line 172, in post
    return super().post(request, *args, **kwargs)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/views/generic/edit.py", line 141, in post
    if form.is_valid():
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/forms/forms.py", line 185, in is_valid
    return self.is_bound and not self.errors
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/forms/forms.py", line 180, in errors
    self.full_clean()
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/forms/forms.py", line 383, in full_clean
    self._post_clean()
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/contrib/auth/forms.py", line 107, in _post_clean
    super()._post_clean()
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/forms/models.py", line 403, in _post_clean
    self.instance.full_clean(exclude=exclude, validate_unique=False)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/db/models/base.py", line 1188, in full_clean
    self.clean()
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/contrib/auth/models.py", line 339, in clean
    self.email = self.__class__.objects.normalize_email(self.email)
  File "/anaconda3/envs/active/lib/python3.7/site-packages/django/db/models/manager.py", line 188, in __get__
    cls._meta.swapped,
AttributeError: Manager isn't available; 'auth.User' has been swapped for 'users.User'

<form action="" method="POST">
    {{ form.non_field_errors }}
    {% for field in form %}
    <div class="form-group">
        <label for="{{ field.id_for_label }}">{{ field.label_tag }}</label>
        {{ field }}
        {{ field.errors }}
    </div>
    {% endfor %}
    {% csrf_token %}
    <button type="submit" class="btn btn-primary btn-lg">送信</button>
</form>

from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth import get_user_model

User = get_user_model()

class SignUpForm(UserCreationForm):
    """ユーザー登録用フォーム"""

    class Meta:
        model = User
        fields = ('email',)

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        for field in self.fields.values():
            field.widget.attrs['class'] = 'form-control'

    def clean_email(self):
        email = self.cleaned_data['email']
        User.objects.filter(email=email, is_active=False).delete()
        return email

class SignUp(CreateView):
    form_class = UserCreationForm
    template_name = "accounts/signup.html"
    success_url = reverse_lazy('')

    def form_valid(self, form):
        user = form.save(commit=False)
        user.is_active = False
        user.save()
        # アクティベーションURLの送付
        current_site = get_current_site(self.request)
        #domeinの取得
        domain = current_site.domain
        context = {
            'protocol': self.request.scheme,
            'domain': domain,
            'token': dumps(user.pk),
            'user': user,
        }
        #templateを呼び出す
        subject = render_to_string('mail/create/subject.txt', context)
        message = render_to_string('mail/create/message.txt', context)

        user.email_user(subject, message)
        return redirect('accounts:SignUpDone')

class SignUpDone(TemplateView):
    """ユーザー仮登録したよ"""
    template_name = 'accounts/signupdone.html'

class SignUpComplete(TemplateView):
    """メール内URLアクセス後のユーザー本登録"""
    template_name = 'accounts/signupcomplete.html'
    timeout_seconds = getattr(settings, 'ACTIVATION_TIMEOUT_SECONDS', 60*60*24)  # デフォルトでは1日以内

    def get(self, request, **kwargs):
        """tokenが正しければ本登録."""
        token = kwargs.get('token')
        try:
            user_pk = loads(token, max_age=self.timeout_seconds)

        # 期限切れ
        except SignatureExpired:
            return HttpResponseBadRequest()

        # tokenが間違っている
        except BadSignature:
            return HttpResponseBadRequest()

        # tokenは問題なし
        else:
            try:
                user = User.objects.get(pk=user_pk)
            except User.DoesNotExist:
                return HttpResponseBadRequest()
            else:
                if not user.is_active:
                    # 問題なければ本登録とする
                    user.is_active = True
                    user.save()
                    return super().get(request, **kwargs)

        return HttpResponseBadRequest()