It is common on new developments for the property to have been built, but the licence to occupy the property not to have been issued by the Council. This could cause a delay in the property being registered. In the meantime you could use the private purchase contract that you have as evidence that the property is yours until the property is registered at the land registry in your name.

I would also suggest as a practical measure, you ask the vendor/developer to give you his specific reason for the delay in writing, in order to ascertain exactly what the cause of the delay is. His explanation for the delay can then be checked with a Spanish lawyer/Solicitor who will be able to confirm whether it is a normal delay, or whether something can be done to facilitate registration of the Spanish property.