I was banging my head with the same problem!
I found something here that worked for me. https://github.com/woocommerce/woocommerce/issues/25895
Just go to Tools -> Scheduled Actions , click and wait to generate new table. That’s it!
thanks blue_life.
this was a relief.
can you help me sort out some other troubles.(not related to this thread).
If you are willing to help me resolve some Nextgen gallery related enhancements,I can mail you my queries.