How to make a selection in a radiobutton group

How do you programmatically make a selection in a radiobutton group? My code  Response.Write(myReader("subgroup1")) ' Shows I am getting the correct value from the table ie "Member"
optSubGroup.SelectedValue = myReader("subgroup1").ToString ' Errors on this line
 fails with a message that the group has an invalid value because the value does not exist in the group. However, it does. "Member" is the first button, both value and text of the button are assigned "Member"

Thanks
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