sum in subform, can't get it into a form(textbox)

[pinstripe]

hi to all,

this problem drives me crazy.

i have in a subform(Datasheet) footer, textbox "Totale"
and in it's controlsource:
=Sum([Stop Km]-[Start Km])

then on a form i have new textbox "Text81"(unbound)
and also combobox which has in it's After_update Event:

If (Me![IzpisPrevoza_Registerska_sub].Visible = True) Then

Me!Text76 = [IzpisPrevoza_Registerska_sub].Form![Text106]
-- this one is working fine
Me!Text81 = [IzpisPrevoza_Registerska_sub].Form![Totale]
-- this one doesn't work
there is no error but my textbox "Text81" remains blank

i did debug it:
first part - "Me!Text81 = " =Null
second part - "[IzpisPrevoza_Registerska_sub].Form![Totale]"
has the corect number(Sum)

any help is need it
thank's

 

[aldior]

use nz(Sum([Stop Km]-[Start Km]))