When trying to enter a new listing, Matrix is not accepting the parcel ID the user is entering.
This usually happens because the user is trying to enter the parcel ID from a field card.
Matrix assigns a unique parcel ID to all properties that is likely different than that you would find on a field card.
Make sure to search Matrix for the correct parcel ID when you go to enter a listing.
Go to Search> Tax Search
Enter just the County, Town, Street Number and Street Name- usually just those 4 fields are enough to find the correct parcel ID.