making sure <Enter> key always works???

[VMI]

If I'm in a multi-line textbox and I'm writing a postal address (ie. write
ist line and press <Enter>, write 2nd line and press <Enter>, etc...) how
can I make sure that the Enter key will always make the cursor jump to the
following line in the textbox? For some reason, and this happens everywhere
except on my development PC (and it's not consistent), if a user's writing a
line and presses the <Enter> key, the program interprets that as the user
pressing another button in the Form (instead of jumping to the next line of
the multi-line textbox). I think it has something to do with where the
focus is on the Form, but as long as the cursor's on the multi-line, an
<Enter> press always has to jump to the next line. How can i make sure that
always happens?

The worst part is that I can't debug it in my dev PC because it never
happens there.

Thanks.