using combox box how to uncheck the radio button

Question

using combo box how to uncheck the radio button.

i have one combo box and one radio button.

 course  combo box

 Radio button.

when i click the combo box, the radio button is to uncheck.

for that how can i do?

my code as follows;

SessAM.Checked = false;

but the above code is not working why what is the mistake i made from my above code.