Topic: Strange error message.. how to resolve?

I got the following error message. This occurred after I tried to invoke a reoccurring invoice, which I may have set up wrong, and I was trying to correct it.

Undefined variable: sub_total in file:
/homepages/31/d322290405/htdocs/forte/sales/view/view_dispatch.php at line 150

What should I be doing to correct or avoid this in the future?

Re: Strange error message.. how to resolve?

Seems that document you want to look into has no line defined, which should not appear normally.
Janusz