Even if it was a grammar issue, grammar can always be learned and corrected. I would much rather start with a grammar problem than a storytelling problem or a flow problem. Grammar is much easier to learn and correct.
And I'm one of those people that started out with bad grammar; I'd forgotten all of my rules from high school. But each time someone corrected me on my grammar, I used it as an opportunity to grow and learn.
And honestly, the person who told you to quit....shame on them. I'd love to open up his/her early writing and take a gander and critique it.
