Can't seem to get Translation to work

I've been using the CustomField successfully in a custom View but I've run into a problem with the output not getting translated.

Normally the following code would display "years" in English and "años" in Spanish...

... some miscellaneous php code ...
print (t('years'));

However, when I display the view in Spanish it gives me "years" instead of "años". Other fields in the View display "años" but not the CustomField. Everything else works fine except the translation in the CustomField. Do I need to insert something into the PHP CustomField to make it work with translation or is this a bug?

Cheers