[web2py] compute field error

[Plumo]

I found when I use the compute field I get this error when inserting via 
appadmin:

ProgrammingError: column "update" specified more than once


def now(record):
    return datetime.datetime.now()

db.define_table('upload',
    Field('data', 'upload', required=True),
    Field('created', 'datetime', default=request.now),
    Field('updated', 'datetime', compute=now)
)


Any ideas?

Richard