@Michael C @UK Rob, sorry for the problems this may have caused. If you have this problem, try saving the keys using the second method. If you go to Tools – Change parameters – and then click on Tags, keys and codes and add the keys and tracking ID in that location. You must ensure that the 3 required fields are complete, the Amazon key, the secret key and the tracking ID.
Once the keys have been saved, you should be able to add products without problems, if you still have problems, send a ticket and we will see the problem. Please provide full login information to get help quickly.