You likely already have an existing WRDS account, so you do not need to register for a class account again. Instead, please simply follow the steps outlined in the Student Guide: Enrolling in a Class Account (Already Have a WRDS Account? How to Enroll in a Class) to enrol in the class you need.
If the instructions in the guide do not resolve the issue, please contact us via email and we will investigate the problem or report it to WRDS for further support.