List Box with Expression - Always one Selected Value disabled ?

[#1]

Hi

I have two list boxes.  List Box (A) and List Box (B)

(A) contains list of values from a dimensions i.e. not an expression.

(B) contains list of values from an expression.

When the sheet is activated I need to force a selection in (B).  The values show in (B) are dependent on what value is choosen from List Box (A).  (A) has 'Always one selected' enabled.  Pressing clear should not clear list box B.

Since I am unable to use 'always one selected value' in list box (B) due to expression is there any other way that I can do this?

Note: List box (B) contains 10 values.  However only 3 of those values are displayed on sheet 1 while the other 3 are displayed 

only on sheet 2.  therefore I am unable to load all the values to resolve this problem.

[danielrozental]

Sometimes it's simple to display a message and have the user make a selection than trying to force a behaviour.

If no value in B is selected you could display a textbox with the message "Please select a value in B", instead of forcing the "always one value selected"