When using the full recovery model backup option, transactional logs will be generated every time there is a transaction being made. The transaction log will keep accumulate until a full, differential, transaction log backup has been made. Only then will the logs be cleared up. In databases where there are high transaction being made, the transaction log can fill up very quickly. You need to make sure there are enough disk spaces on the server for the transactional logs. Your database will not be able to take in any more transactions if the transactional log is filled up.