Rick,
I don't why it isn;t working for you now but I do have a suggestion to make it simpler.
create cursor MyCursor1 (Mem1 m, Mem2 m)
append blank
append memo mem1 from (lcMyTextFile) overwrite
append memo mem2 from (lcOtherTxtFile) overwrite
if !empty(MyCursor1.mem1) && don't need _tally here .and. _tally != 0
thisform.indexes.controlsource = "MyCursor1.mem1"
endif
if !empty(MyCursor1.mem2)
thisform.fields.controlsource = "MyCursor1.mem2"
endif
thisform.refresh()
erase (lcMyTextFile)
erase (lcOtherTxtFile)