How to make phrases from VB 3.0.x still usable?

[bibicax]

When I update my VBB 3.5.x, some old phrases from VBB 3.0.x no longer work anymore. Instead of showing the value, now the variables shows their name, $vboption[bburl] - for example. Some phrases still work, such as "Email subject" or "Email body", but the others such as "Front-end error message" don't.

How to do code modification to make my VBB 3.5.2 parse those variables as their value?

Tks a million!