A relationship type of "Variation" was provided for an item with no VariationTheme. For steps on how to fix this, see http://sellercentral.amazon.co.uk/gp/help/23921
If you submit a tab-delimited inventory files, this error occurs when you provide a RelationshipType value for a child product but omit a VariationTheme value. Child products with a RelationshipType must also have a VariationTheme. To resolve this error, resubmit your inventory file with a valid VariationTheme for the child products.
If you post relationships feeds (XML), this error occurs when one of the SKU values you provide in a Relationship element was not previously assigned a VariationTheme in a product data feed. To resolve this error, you should do the following: