Hello @ronda,
In this post here, which is the same error, it would appear: Crossref plugin error for depositing articles - #7 by bozana
One of our developers who works closely with Crossref plugin recommends upgrading to OJS 3.3.0-5 - since there may be fixes in that version of OJS (as well as the Crossref plugin) that may address these issues - is that possible for you to upgrade? That may help to resolve the issue, or, at the very least, get better error/status messaging.
-Roger
PKP Team