stuck on preparing to copy

Hi there, I am currently trying to transfer everything from one external hard drive to another. After some digging, i found that when transferring the libraries over simply doesn't work. It will say it is preparing to copy but doesn't change at all. When trying to cancel, it doesn't cancel. It is like stuck in a loop. It will say canceling but won't actually cancel. That being said, the only way to actually get it to stop canceling is to hard shut down the mac. Any idea what this could be?