There are two plugins in our plugin list that would help. One institutes a ban. The other allows for bans, suspensions and warnings which is more versatile of course. You can read more on the lalter here:
I assume by your mention of the 'Warnings Button' that you actually mean the 'Warnings and Suspensions' plugin and not the 'Bans' plugin. Is that correct?
Moderator interaction with this plugin is not in the admin section but in the front-end. When on a post made by an offending user, a moderator can use the forum tools button to select the Ban, Warnings and Suspension options.
I can replicate the issue with being unable to open the panels from within the admin. This looks like it might be an issue caused by the recent WordPress update which we will investigate immediately. It was working OK prior to this I believe. We will come back on that one when we have worked out what the cause is.
Admin Links and Admin Panel Access:
OK - Admin Links (in the admin bar plugin) - are for admins only and can not be turned on for moderators. Access to forum admin panels for moderators can be done in the admin side of your website. If you go to the forum section > Admins > Manage Admins, you can turn on which forum admin sections you want your moderators to see and work with. They will be limited to those sections.
The Forum Tools:
As said - these are the items that a moderator should really be working with in the front end and when it comes to this specific plugin - there is nothing they can not do here that can be done in the back end admin section.
Accessing the Bans, Warning and Suspension Admin Panels:
Until we get a fix in place for this I can give you a workaround. Go to the website admin and select the forum link from the WP menu down the side and click on 'Warnings' (which is probably at the very bottom). This will open the Warnings Options panel. Then you can select one of the other panels in the section. What fails is then trying to open a different one. But you can get to each one using the above method. Hope that helps.