When processing a debit transaction you may receive an "Invalid Mac 499" declined error.  This error only applies when processing a debit sale, credit card transactions works without an issue.


  1. Reinstall dsiEMVClientX or update dsiEMVClientX.  A lower version dsiEMVClientX could also cause this issue. 
  2. Restart the computer 
  3. Perform a Parameter download and Key change
  4. Test and Debit transactions should now operate