One of the most common grammatical errors I see on the web is faulty parallelism. I assume most writers are not even aware of the error. Faulty parallelism exists when two potentially related actions differ in structure. Let me illustrate. I enjoy reading books, going for walks, and photography. You probably noticed the difference between the first two and the last one, the last one being a noun and the others being specific actions.
Link: What is faulty parallelism?