I have reset your client account password to be the same as your forum account. It had been changed.
Can you let us know what browser and operating system you are using?
Are you clicking the swap link? The are two methods to add a forum account under a client account. "Create new" and "Swap." To get the "username in use" error you must be trying to create a new forum account.
Your domain is changing back to urban-explorer.x10hosting.com now.
What date did urban-explorer.x10hosting.com stop working for you? Please give a numerical date as close to when you noticed it as possible, along with your timezone.