[web2py] list:reference problem?

I have a field with the 'list:reference xxx' type. Using it gets the following error (I think): Traceback (most recent call last): File "C:\Users\Andre\Documents\web2py\gluon\restricted.py", line 188, in restricted exec ccode in environment File "C:/Users/Andre/Documents/web2py/application

[web2py] list:reference problem?

The model: db.define_table("gr01", Field("service_provider", db.service_provider, requires=IS_IN_DB(db,db.service_provider.id, '%(name)s')), Field("trainer",'list:reference db.trainer', requires=IS_IN_DB(db,db.trainer.id, '