@Michael C @UK Rob, sorry for the problems that could have caused. If you experience this problem, try to save the keys using the second method. If you go to Tools – Change Settings – then click Tags, Keys and Code and add the Keys and Tracking ID to this location. You must make sure that the 3 mandatory fields are filled in, namely the Amazon key, the secret key and the tracking ID.
Once the keys are backed up, you should be able to add products without any problem. If the problem persists, send a ticket and we will investigate the problem. Please provide complete login information to get help quickly.