Domain attachment problem

[diwaker0]

I have problem with my domain. I added shop.lexioninvest.com to my account and then i added lexioninvest.com to my account, but now i am not able to add shop.lexioninvest.com again to my account. Then i added buyit.lexioninvest.com to my account and now i am not able to add shop.lexioninvest.com and lexioninvest.com, means the address which i add one time to my account i am not able to add again to same account. Please help how to fix this problem.
Thanks
Admin LexionInvest.com