You owe more than the property is worth. You do not have access to enough money to clear the debt.
Example Recent Solution:
Customer had a property which was worth the same as his current mortgage however the mortgage redemption figure was £8,000 plus the other costs of estate agent, Solicitor fees etc .
He did not have the money to pay the £11,000 so we arranged the following solution:
We would purchase the property for the full market value in the future when the price had increased to clear the debt and in the meantime we would pay his monthly mortgage enabling him to take the new job he had been offered overseas.
No large fees for the seller and proper legal contracts through a Solicitor.