I've filled out the details required and click register a box pops up with could not add object.

Is there something im missing or doing wrong?

Database issues or something along that spectrum.

How do you mean "register clan"?

You can create a 'Team' on Gametracker (you already have one).
I have created a team, and deleted it, without any issues.

I am not aware of 'registering a clan' aside from assigning your team to your server, which is then described as 'Clan Info' on the server page.

all good