"You are attempting to change an identity attribute for this SKU. To proceed, please delete this SKU and recreate the SKU with the appropriate identity attribute. For more information and detailed instructions, see: http://sellercentral.amazon.com/gp/help/23191"
When this error appears, it means that there are product details in Zentail that do not match the details that Amazon has on file for this SKU.
Amazon thinks that the SKU is being listed to the wrong ASIN, or Amazon is trying to prevent you from possibly updating this ASIN with incorrect data.
Unfortunately, Amazon does not always provide enough context to easily identify the specific information that is causing the issue exception to. Occasionally, this exception can be due to a UPC conflict (i.e. your product's UPC does not match the product's UPC on Amazon).
Solution: Confirm this is the correct ASIN to list your SKU to. Look through the product data in Zentail and see if there are any small, trivial details that deviate from the information on the ASIN page.
If you feel comfortable making a minor change to your data in Zentail to resolve this issue, then go for it - and monitor the SKU to make sure it gets listed. Alternatively, you can create an Alias SKU.