Failing to Understand Basic Intellectual Property Law
Regardless of what type of lawyer you are (litigation, business, or whatever), if you deal with the technology ecosystem, you must have a basic understanding of patent, copyright, trademark, and trade secret law. Go buy a book, talk to a friend, or search the internet to have at least a basic sense of the differences between these four areas. Your clients will know a lot about this subject matter. Don't make them teach you. It doesn't look very good.