General ("financial") Durable Powers of Attorney (DPOAs) are very useful documents that every competent adult should have. DPOAs can be used to manage one's property and affairs in the event of incompetency, avoiding the need for a court proceeding to determine incompetency and appoint a guardian. This can save thousands of dollars in attorneys and court fees, not to mention much time and trouble.
However, what many people do not realize is that DPOAs are no longer valid after the person who signed it (the principal) dies. Thus a DPOA cannot be used for any purpose after the death of the principal, including signing checks or accessing a safe deposit box. If the bank doesn't know that the principal has died, the agent under the DPOA may not be prevented from taking these actions, but doing so could result in civil or criminal liability.
So, if you are the agent under a DPOA, DO NOT take any action using the DPOA after the principal dies. If you do, you may very well create a mess that you will have to pay a lawyer to clean up for you. My firm is doing that right now for at least one client.