Sentence examples similar to was error from inspiring English sources

No, "was error" is not a correct or usable part of a sentence in written English.
It is missing a grammatical subject and verb, and it does not make sense on its own. However, "was an error" is a common phrase used to describe something that was incorrect or mistaken. Here is an example: "The teacher's calculation was an error, which resulted in incorrect test scores for the students."