no database or no database description.

CB Tools / Check CB plugins database:

How do I fix the following?

CB plugin "JComments Tab": no database or no database description.
CB plugin "CB JEvents": no database or no database description.
CB plugin "CB AEC Membership Tab": no database or no database description.
CB plugin "CB LastViews Tab": no database or no database description.

I've uninstalled one and reinstalled it (LastViews 1.2) but same result.

CB1.9RC

There's nothing to fix. Those plugins simply don't have an empty database tag in their XML files so that's what CB displays if the tag is missing entirely.

And those plugins, although do have an entry in Admin / CB / Tabs, do not show on the users profiles on the front end - Public, logged in, or edit view.

So why do these not show? Is it a coincidence?

I've PM'd you a super admin login for my site to go have a look for yourself and let me know your thoughts.

That tool check message is irrlevant to a tab displaying. A tab could be hidden due to ACL, could be a condition on the tab from CB Conditional, edit display could be disabled by CB Privacy, they're all also Plugin tabs so if the plugin isn't enabled in CB > Plugin Management then they'll also be disabled.

Just working on the JComments tab for now. There is a "Comments" tab, but this one does not show my comments on articles. The "My Comments" tab is configured exactly the same as the "Comments" tab (both are linked to JComments), but this tab does not show.
I've disabled allsorts. I really would appreciate you having a little look on this one so I can at least see that it can work.

You need to contact JComments for support on their plugin, sorry; we don't review and fix 3rd party plugins. It's possible there's an issue in the plugins code it self, maybe just an IF statement, causing it to not render any tab content which would cause it to render no tab.