Thanks Jim.
Specifically, a_tmp is a two-dimensional array containing codes and descriptions. It is the RowSource of my combobox. The button.click event code below works fine to display the description for 'COD1' in the combobox. However, when I then try to select by picking from the dropdown list, I get 'feature not available' error.
Any ideas most welcome.

KEN='COD1'
if ascan(a_tmp,ken)<>0 then
x=ascan(a_tmp,ken)
y=asubscript(a_tmp,x,1) &&returns row
thisform.pageframe1.page1.CBOX_tmp.value=a_tmp(y,1)
endif