The variation specific used for pictures on the Сhannel has been removed. A relevant variation picture set must be sent

This error usually occurs when a Variation Specific attribute isn`t chosen in the 'Change Images for Attributes' section of the description policy. 

Please check the product's Variation Specific attributes.

Ensure that the attributes are selected under Change Images for Attributes.

As an option to cover all Variation Specific in the Change Image for Attributes section, you can select all of the variation attributes in this section.