What is an error in English?
The concept of language errors is a fuzzy one. I’ll leave to linguists the technical definitions. Here we’re concerned only with deviations from the standard use of English as judged by sophisticated users such as professional writers, editors, teachers, and literate executives and personnel officers. The aim of this site is to help you avoid low grades, lost employment opportunities, lost business, and titters of amusement at the way you write or speak. But isn’t one person’s mistake another’s standard usage?
Often enough, but if your standard usage causes other people to consider you stupid or ignorant, you may want to consider changing it. You have the right to express yourself in any manner you please, but if you wish to communicate effectively, you should use nonstandard English only when you intend to, rather than fall into it because you don’t know any better.