Hi
The problem is related to the thirdparty extension, I think MASS products update.
I have made a small fix in owc_productsalecostprice.xml at line 166, see comment above.
Now it is working but when you download a new update, this change must be applied again.
If you like my extenstion and support, please leave a comment and rate my extension at
https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=28041&filter_search=costprice
Best regards
Dennis
Best regards
Dennis