Subscribe2 changing default email digest subject

I would be very reluctant to use code from a three-year-old thread in a current installation. Also I don’t see that plugin in the repository any more. We aren’t able to help much with plugins that aren’t there.

You might want to check what’s going on with its development at subscribe2 dot wordpress dot com. If there’s no clue there on how to proceed, you may want to find something else to take its place.