django-autocomplete-light: invalid literal for int() with base 10

I am using autocomplete-light to suggest names in a form field. It is go well in the createView ,but when I want to change a value in the very same field it tlod me “invalid literal for int() with base 10:” error. I’v been read all the related issues and did not have a clue.Can some one help me.

#forms.py
class CaoZuoPiaoForm_zhengling(forms.ModelForm):
    yunweizhan = forms.ModelChoiceField(YunWeiZhan.objects.all())
    nipiaoren=forms.ModelChoiceField(queryset=UserProfile.objects.all(),widget=autocomplete.ModelSelect2(url='bdgqpt:name-autocomplete'))
    shenpiaoren=forms.ModelChoiceField(queryset=UserProfile.objects.all(),widget=autocomplete.ModelSelect2(url='bdgqpt:name-autocomplete'))
    caozuoren=forms.ModelChoiceField(queryset=UserProfile.objects.all(),widget=autocomplete.ModelSelect2(url='bdgqpt:name-autocomplete'))
    jianhuren=forms.ModelChoiceField(queryset=UserProfile.objects.all(),widget=autocomplete.ModelSelect2(url='bdgqpt:name-autocomplete'))
    zhibanfuzeren=forms.ModelChoiceField(queryset=UserProfile.objects.all(),widget=autocomplete.ModelSelect2(url='bdgqpt:name-autocomplete'))
    falinshijian = forms.DateTimeField(widget=DateTimeWidget(usel10n=True,bootstrap_version=3,
        options=dateTimeOptions,attrs=dateTimeAtts),required=False)
    kaishishijian=forms.DateTimeField(widget=DateTimeWidget(usel10n=True,bootstrap_version=3,
        options=dateTimeOptions,attrs=dateTimeAtts),required=False)
    jiesushijian=forms.DateTimeField(widget=DateTimeWidget(usel10n=True,bootstrap_version=3,
        options=dateTimeOptions,attrs=dateTimeAtts),required=False)

    class Meta:
        model = CaoZuoPiao
        fields = "__all__"
    def __init__(self, *args, **kwargs):
        super(CaoZuoPiaoForm_zhengling, self).__init__(*args, **kwargs)
        self.helper = FormHelper(self)
        self.helper.form_class = 'form-horizontal'
        self.helper.label_class = 'col-md-4'
        self.helper.field_class = 'col-md-8'
        self.helper.layout=Layout(
            'yunweizhan',
            'biandiansuo',
            'leibie',
            'bianhao',
            'caozuoneirong',
            'nipiaoren',
            'shenpiaoren',
            'falinren',
            'falinshijian', 
            'kaishishijian',
            'jiesushijian',
            'caozuoren',
            'jianhuren',
            'zhibanfuzeren',  
            'bushu',
            'zhuangtai',                   
            ButtonHolder(Submit('submit','Submit')),
            )

#views.py
def caozuopiao_update(request, id=None):
    if not request.user.is_authenticated():
        return render(request, 'bdgqpt/login.html')
    else:       
        instance = get_object_or_404(CaoZuoPiao, id=id)
        form = CaoZuoPiaoForm_zhengling(request.POST or None,instance=instance)
        title="Modify"
        if form.is_valid():
            instance.save()
            messages.success(request,"Success")
            return redirect('bdgqpt:caozuopiaohomepage')
        context = {
            "form": form,
            "title":title,
        }
        return render(request, 'bdgqpt/caozuopiao/caozuopiao_update_form.html', context)

caozuopiao_update_form.html
{% extends 'bdgqpt/base.html' %}
{% load crispy_forms_tags %}
{% block title %}{{title}}|{{block.super}}{% endblock %}
{% block liangpiao_active %}active{% endblock %}
{% block body %}
<div class="container-fluid">
    <div class="row">
        <div class="col-sm-12 col-md-6 col-sm-offset-3">
            <div class="panel panel-default">
                <div class="panel-body">
                    <h3>{{title}}</h3>
                     {% if error_message %}
                        <p><strong>{{ error_message }}</strong></p>
                    {% endif %}
                    {{form.as_p}}
                </div>
            </div>
        </div>

{% endblock body %}