When you select a radio button format for a field, you must also select a value list to use with it. You can click the pencil icon in the Inspector to create that value list or you can select Manage | Value Lists to create it, then select it in the inspector,
Assuming that you don't want to see radio buttons labeled 1 and 0 in your field, you'll also need to replace the 1's and 0's with the text you specify in your value list such as "yes" for 1 and "no" for 0. Replace Field Contents can use this calculation to make that change to your data:
Case ( YourTable::YourField = 1 ; "Yes" ;
YourTable::YourField = 0 ; "No" )
This calculation will leave the field empty if there is neither a 1 or a 0 in it.