CRM Upgrade Code Mystery

We have just upgraded Dev from CRM 3.1 to 4.0

I have a problem where something that was working is now not.

Debugging our non-upgraded CRM system alongside our upgraded CRM system I got to a line of code :

CALL SUBSCREEN screen_3000_resizing_area.

In the upgraded version this goes to program SAPLBUS_LOCATOR

In the non upgraded version the same line of code takes me to SAPLBUPA_DIALOG_JOEL

Can anyone enlighten me how this can be so ?

Many Thanks

David