I'm having this problem on my MacBook Pro. (Still on El Capitan.) It keeps telling me I have updates, but then it won't let me update them.
First I get:
The iTunes Store is unable to process purchases at this time.
Please try again later.
I click OK and this pops up:
We could not complete your request.
There was an error in the App Store. Please try again later.
Later never comes. I tried making the updates through Purchases, but that makes no difference. I've signed out, signed in, restarted, updated payment options and verified everything verifiable. This has been going on for days. Super annoying.