ASP.Net Repeater, RadioButton, GroupName doesn’t work
The issue is Radio Buttons Are Not Mutually Exclusive When Used in a Repeater Server Control.
This is a known issue of ASP.NET template databound control(such as repeater, DataList …). When you put RadioButton in such control's template, since its "groupName" is assigned a unique value each row,. Here is the public kb article document this issue: