As far as I understand, djhomeschool got it correctly. Essentially if your transaction was considered as dust by other (almost every) nodes then it won't get transferred, therefore it won't reach the mempool.

However, judging from your case, I assume you're consolidating a lot of small input and then send it as a single output, is this right? Then it should not be considered as dust imo as long as your fee is high enough. Anyway, you can read more about this case here: https://bitcointalk.org/index.php?topic=2637574.0

Maybe one of your input is already spent. Can you post any raw data?