Exception Type: TemplateSyntaxError Exception Value: Invalid filter: 'css_class'

[camdenroberts]

I am getting the following error:

Template error

In template c:\users\wings\fg-env\lib\site-packages\django_forms_bootstrap\templates\bootstrap\field.html, error at line 8
Invalid filter: 'css_class'

1 {% load bootstrap_tags %}
2
3 {% if field.is_hidden %}
4 {{ field }}
5 {% else %}
6

7
8 {% if field.label and not field|css_class == "checkboxinput" %}

TemplateSyntaxError at /naturel/naturelcalendar/calendar/month/calendar/

Invalid filter: 'css_class'

Request Method: GET
Request URL: http://localhost:8000/naturel/naturelcalendar/calendar/month/calendar/
Django Version: 1.3.3
Exception Type: TemplateSyntaxError
Exception Value:

Invalid filter: 'css_class'

Exception Location: C:\Users\Wings\fg-env\lib\site-packages\django-1.3.3-py2.7.egg\django\template\base.py in find_filter, line 320
Python Executable: C:\Users\Wings\fg-env\Scripts\python.exe
Python Version: 2.7.3
Python Path:

['C:\Users\Wings\bumpmd\apps',
'C:\Users\Wings\bumpmd',
'C:\Users\Wings\fg-env\lib\site-packages\setuptools-0.6c11-py2.7.egg',
'C:\Users\Wings\fg-env\lib\site-packages\pip-1.1-py2.7.egg',
'C:\Users\Wings\fg-env\lib\site-packages\django_avatar-1.0.5-py2.7.egg',
'C:\Users\Wings\fg-env\lib\site-packages\pil-1.1.7-py2.7-win32.egg',
'C:\Users\Wings\fg-env\lib\site-packages\django_crudgenerator-0.0.7-py2.7.egg',
'C:\Users\Wings\fg-env\lib\site-packages\django-1.3.3-py2.7.egg',
'C:\Windows\system32\python27.zip',
'C:\Users\Wings\fg-env\DLLs',
'C:\Users\Wings\fg-env\lib',
'C:\Users\Wings\fg-env\lib\plat-win',
'C:\Users\Wings\fg-env\lib\lib-tk',
'C:\Users\Wings\fg-env\Scripts',
'C:\python27\Lib',
'C:\python27\DLLs',
'C:\python27\Lib\lib-tk',
'C:\Users\Wings\fg-env',
'C:\Users\Wings\fg-env\lib\site-packages']