dtoc() is a standard keyword, which should be recognized. Try separating your command into two parts. Perhaps this helps you in debugging:
temp = thisform.txtdt.value
clist1 = dtoc(temp)
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
