Please go to RevSeller.com, click on “My Account” and then click on “Amazon MWS.” That page will tell you if you need to add or update your MWS credentials in order for the extension to work.
Please go to revseller.com in your Chrome browser, then click logout, then log back in. Then check an Amazon product page and see if it works.
Go to chrome://extensions/ Make sure RevSeller is there, and make sure on the right side the checkbox is checked so that RevSeller is enabled.
Go to chrome://extensions/ Find the Revseller extension and click the trash icon to the right to uninstall. Go to RevSeller.com, click "My Account," then click "Download Extension" and follow the instructions there.
Go to chrome://extensions/ and disable all other extensions (uncheck them on the right side) except RevSeller, then try and reload an Amazon page and see if it works then.