The error that you see is given by Windows Installer, it appears because by design the OS does not allow having a radio button group UI control with only one button,
this would be pointless, as the user would be forced to select the same button, therefore it would not be a choice but a hard-coded option. For this is recommended you delete all the radio buttons and the group and just set the property "MaintenanceTypeOption" to the string "Remove" using a "SetProperty" Init Event.
This is the property which is set by the radio button group, setting automatically is identical with the user selecting "Remove".
Another option, which I don't recommend, is to have Enhanced UI set to "Always" from Themes page. This will make the EXE setup to always control the MSI dialogs, which it ignores this type of errors.