Back to the form which fails, there in OnShow back some lines before the RadioGroup1.Items.Add is aA radiogroup within a radiogroup? Why that? Do you want to have a group of radiobuttons within a group of other radio buttons? Or what else do you want to achieve?
RadioGroup1 := tRadioGroup.Create(NIL).
RadioGroup1 without a Create worksAnother mystery... Without creating a control it certainly will NOT work.