errors.add_to_base translation missing: en, activerecord

In my model I am using errors.add_to_base:

errors.add_to_base "Error 1"

This works fine.

If I do this twice:

errors.add_to_base "Error 1"
errors.add_to_base "Error 2"

I receive the message:

translation missing: en, activerecord, errors, models, modelname,
attributes, base,

as part of my error messages.

Anyone know how to get rid of this?

Many thanks,

Mike