EIN [xxxxxxxxx] does not match with an existing employer's EIN number.

This validation error tells you that there is an EIN in your file that does not match an EIN in your Employer Roster. Use the row information from the error message to locate the EIN in your file and check it against the information in your roster. You may need to add a new employer to your roster, or contact the fund office to confirm that the EIN in your file is correct.