Since others are still able to register successfully (as seen here), there is no general issue with the form. I’d need a reproducible case to help 
However, since you already have an account, the simplest solution will be that you simply post in the registration topic. This is where everyone’s registration post goes, so just have a look at these and post your own in a similar format. For our software that will look the same as when registering through the form, and will count as you being registered for participation.