Error: Invalid_key_or_ref: Import failed for SF record id <the id is specified>

Error:

Invalid_key_or_ref: Import failed for SF record id <the id is specified>.  
Reason: Invalid price reference key -1 for item.

Meaning:

This means that the product(s) on the Opportunity has not been synced to a NetSuite item.

Resolution:

Find the NetSuite id.  Edit the Salesforce Product to include the NetSuite item id.  Edit the NetSuite item to include the 18-character Salesforce id.