It would appear that your records are being shown within a "portal" (a view of related records) and as far as I know (someone else might want to clarify this) but, the scroll wheel won't work within portals.
If you where to view these records within the "child" table, in list view, I believe the scroll wheel should work.
Thanks for the reply Peter. I don't know if this helps but I can use the scroll wheel if I change from "form" view (one client record at a time) to "list" or "table" view - I can then scroll (using the wheel) though the list of clients. The problem remains that I can't get the scroll wheel to function when I'm in a client record and want to scroll down the contact fields in that record as in the screen shot.
I just looked up what you mean by "child" table...I don't think my system's been set up that way.
Anyway, it's a pity if the simple functionality of the scroll wheel I described can't work here.