Calculated Textbox using Invisible values

[Guest]

I have a calculated textbox with data source
=Nz([A],0)+Nz(,0)+Nz([C],0)+Nz([D],0). Any one or more of the textboxes
B, C, D can be invisible. Everything works fine at data entry time. But
when I recall the record for edit, the calculated field is #Error. I tried
removing Nz(,0)+Nz([C],0)+Nz([D],0) from the expression as B, C and D were
invisible for the particular record to be editted and the error went away.
Any thoughts as to how to get rid of the #Error when attempting to edit the
record? Or what the problem is? Are invisible fields acceptable in
calculated unbound textboxes? One further note, textboxes A, B, C and D are
on separate tab pages.

 

[Stu]

Upon further investigation Fields A, B, C and D apparently may not actually
exist if they are invisible in "Form_Load". Consequently I could not find
anyway to reference their properties. I ended up doing a DLookup for each
field to see if data existed in each of the 4 separate tables in which the
fields exist. Then I created a data source string adding only fields that
exist. Case Closed.