1)  The value for MATCH_COMPANY on the Transaction_Soft_Credit record was no longer a valid Briefname. The Briefname may have been deleted or altered. 

Examine the match_company field, and either fix the status or fix the Briefname on the Soft Credit.

OR

2) The account has a matching gift relationship with a blank Name_ID.

View the Relationship and select the correct name - Name ID will be populated this time.