All available estates (houses, castles, apartments, shops, sheds etc.) or land areas are traded within the Entropia Universe, for example via the auction system, in shops or via PvP trade.

1. Make sure you have the Estate Deed in your carried inventory.
2. Check the items info of the deed to verify that you are standing at the right estate terminal.

If you still cannot claim the estate after trying the above suggestions, please contact Entropia Universe Support.

This is probably due to the fact that you have more than 8 light sources in that room. At the moment, this is the maximum amount of light sources you can have active at the same time.