"object required" error

first form

private sub HpBtn_click()
unload me
call fdata.main(0, false) 'error occured
end sub

fdata form

sub main(page as integer, author as boolean)
  load me
  if (page = 0) then
    multiplepage1.value = 0
    DeleteBtn.visible = author
    AddBtn.visible = author
  else if (page = 1)then
    multiplepage1.value = 1
    'etc

"object required" error was popped up.
why that happen??