If you radio button are in the same group, checking one automatically un-check others. In this way, you need the handler for only one radio button. The second one could be redundant or destroy result of the first one. Remove it.
Besides, what are you doing?!
Who compare a
?! The result is exactly same very Boolean! Who assign another
under if? Please, think a bit before coding, just to understand how ridiculous this is. Do it this way:
txtrb.Enabled = !RadioButton1.Enabled;
Simple, isn't it?