Do not worry if you are due to make a second IMI payment in September and have not yet been able to make the payment, because in 2013 the dates for payment of your IMI tax (council tax) have been changed.
When the amount of your tax is under 250 euros, the payment is done in one instalment only in April, but when the amount due is between 250 and 500 euros, the payment is done in two instalments, one in April as before, and the second has been moved to November instead of September.