Restrict choices already selected from a repeat group

I have tried applying the same concept in my form but if I change the response it does not take off the error message. In the below image, I tried selecting visit 3A and then when the error message showed up, I changed the option to Visit 3B, However, the error message does not disappear.

Can you please have a look at the form and let me know how to rectify this.

ChemotherapyForm.xls (147 KB)

Appreciate any help.

Regards,