Occasionally there can be sync errors when donors/contacts are deleted or merged in Salesforce and we still reference the old data.
To correct this, you can go to the admin panel -> Settings -> Integration Options -> Salesforce and under the "Advanced" Salesforce section, click the "View/Edit Synced Records" button.
Once you locate the errored Donation records, you'll want to select them and in the "Mass Action" drop-down click "the "Resync" option.
Note : Please check Salesforce/Causeview and make sure all the records you are trying to push are not in SF. Resyncing already pushed records might create duplicate records.