MS Unemployment Report will not upload to ReEmployMS

Mississippi (MS) ICESA file is being rejected when uploading to the MSDES (Mississippi Dept of Employment Security) website, with the message:
The file doesn't conform to the specified format or contains invalid data. Verify the content and upload again.

• Payroll
• Mississippi
• MS Unemployment Report

An incorrect account number was entered in the MESC Account field when the report was created.

Enter the correct MESC Account number, which should be ten-digits long.

• The MESC Account in Munis is called the Employer Account Number (EAN) on the MDES ReEmployMS employer portal.
• The error message above is generic and may have many other triggers.