I ran into this issue also with the latest version of satchmo and sorl-
thumbnail. According to the sorl-thumbnail documentation, the tag
needs to be closed like so:
{% thumbnail item.image "100x100" crop="center" as im %}
<img src="{{ im.url }}" width="{{ im.width }}"
height="{{ im.height }}">
{% endthumbnail %}
It is quite likely you are (as am I) using code that expects an older
version of sorl-thumbnail.
http://thumbnail.sorl.net/examples.html
Options are possibly: use an older version of sorl-thumbnail, or
update templates.