This error indicates that the eBay Condition field is missing from your listing or you are using an invalid eBay condition. To resolve this error, please select the appropriate eBay condition for your SKU. This attribute is in the General Info tab of the User Interface:

Please note that this field has specific valid values based on the category. If you are importing this field through the import / export feature, please use one of: New, New other (see details), New with defects, Manufacturer refurbished, Seller refurbished, Like New, Used, Very Good, Good, Acceptable, For parts or not working, used, new, refurbished, recertified, New with tags, New without tags, Pre-owned

Again, the appropriate eBay condition depends on the category. If the eBay condition is not valid for the current category, you will see a critical issue on this SKU: