The recent change in djangoforms breaks the FileField.
i filled a issue here
http://code.google.com/p/googleappengine/issues/detail?id=637
Here is a temporary fix works for me
django.newforms.forms.BaseForm.full_clean() about line 202
if isinstance(field, FileField):
#initial = self.initial.get(name, field.initial)
#value = field.clean(value, initial)
value = field.clean(value)
this can be problematic if you use set a initial data for FileField