10000176 
Message
Enter valid date in "Valid Date From" field
Diagnosis
In the 
Business Partners 
Business Partner Master Data 
path, on the Accounting tab, on the Tax subtab, you have attempted to update an existing
business partner or add a new one. If the Tax Exemption Letter field is populated, the Valid Date From field must also be filled in.
Procedure
In the Valid Date From field, set a valid date value.