Make sure you scroll down and check all of the little boxes for individual documents you are accepting. After the little boxes are all checked, the big Accept button should be clickable.
Please check that the postal code is filled in on your RCA WRS account, and matches the postal code of the credit card you are using. To see that information, go to My Account, scroll down to the Contact Information section, and inspect the Address table.
RCA (Rowing Canada Aviron) and RBC (Rowing BC) are the national and provincial associations governing rowing. They require that all participants pay a small annual fee, once per Program Year (April 1 to March 31). This fee is set by RCA & RBC, and goes directly to them to support rowing in Canada and BC.