New MultiTerm problem - cannot edit entries - Value cannot be null error

Having had great help from Walter already today, now I can run MultiTerm. However, I now have a new problem - when I try to edit any entries, I get this box:

This same box pops up if I try to make an entry on-the-fly in Studio 2015. It's frustrating, because I find this feature so useful.

I hope someone can help. Many thanks in advance.

Susan