If the commenting system, HaloScan, is giving you “The Service is not available; try again later” when you try to publish your comment, try this: right-click your mouse, and when the dialog box opens, choose “Back.” The HaloScan comment box should re-open with your comment intact. Click “Publish” again. That should fix it.
This has been an on-going issue with HaloScan and probably related to high volume.
(Thanks to Faithful Correspondent for the title.)