Periodically eBay requires you to update your token. This also happens when you change your password or make other eBay account changes. Updating your token in inkFrog is extremely easy.
Simply login to your account and visit the 'Settings--> eBay Account' section from the left navigation menu. From here, click on the key icon that is in the same row as the eBay account username you want to update, then follow the on screen prompts.