Firstly, IIf takes three arguments, not two. It works like this:
IIf( <some condition>, <value if condition is true>, <value if condition is
not true>)
It is intended to return a conditional value, and is not appropriate for a
validation rule.
You could use the validation rule like this:
Validation rule: >=[tFrom]
Validation text: "Time to must be higher that Time from"
Personally I would not do this as it could be restrictive and annoying for
the user. For example, the user might have entered a [tTo] value earlier
than [tFrom], intending to then change the [tFrom] value to something
appropriate.
A better approach, when validating one field value relative to another, is
to use the Form_BeforeUpdate event procedure:
If [tFrom] > [tTo] Then
MsgBox "Time to must be higher that Time from"
[tTo].SetFocus
Cancel = True
Exit Sub
End If
If you are not saving a record, but are using values in unbound controls to,
say, filter a report, then the same code should go in the Click event
procedure of the command button that launches the action.
