The error occurs for the items which were listed with another listing duration than Good Til' Canceled initially. After the forced switching of all the listing duration types to GTC, the inactive items need to be resubmitted with the new listing duration.
To get such products activated on eBay again, you would need to List them anew. Make sure to adjust M2E Pro duration settings in eBay > Configuration > Policies > Selling Policy.
Learn about the new eBay billing cycle for fixed-price GTC listings in our article.