This error means that the destination you are trying to ship to requires EEI in order for customs to allow the shipment.
To resolve this, you have 2 options:
File for EEI: You will need to contact FedEx in order to file for EEI. Below is a link to FedEx.com explaining how to go about filing for this. ShipStore system does not automatically file for EEI with any carriers currently. This is something you as the customer will need to set up with the Carrier and cannot be removed or tampered with by the ShipStore system updates or upgrades. 
Exemption: If your shipment is exempt from filing for EEI for this shipment, follow the below steps in the system to bypass the error:
- International Options --> Commodities --> ECCN: To get to this field, you will need to click the blue options button next to each record in the Commodities table, then enter “EAR99” in the ECCN field at the bottom of this window.
- International Options --> AES Exemption code: This is the field where you will need to enter the exemption code that you see below. To make the field available, you will check "Eligible for EEI/AES?", then you'll select Shipper Filed for the EEI Filing Type, then AES Exemption for EEI Filing Type (Sub), then you will enter in your AES Exemption Code (i.e. NO EEI 30.37(a))