Your block/ignore list has a limit. If you reach that limit, whenever you try to add another ignore, you will see “unable to ignore [name].”
You will need to clear out some older entries to make room to add more:
- Exit to the BNet launcher.
- Click the “Friend Settings” button top right.
- Click “Friend and Chat Settings” in the menu that appears.
- Click the “View Block List” button.
- Click the name to remove and click the “Unblock” button.
- Click the “Done” button at bottom right to close the list, then do it again to close the main settings window.
- Start the game, and now you will have the ability to block/ignore, until you run out of room again.
Not ideal, but it works. Please bump the thread if this helps you, since this question comes up all the time. Let’s try to keep it visible in the post list for others to see.