All I did was clone the imperial race and add a few things to them for some npcs and somehow the voice got changed to the name of the new race, so now it has "I have no greeting". I changed it back to use the imperial voice but now it doesn't work. Is there any way to add the stock imperial voices back to these npcs?

Is this a playable race? All dialog is inaccessible to non playable races. The shortest way to restore their access to the dialogue is to make your race playable obviously. Some folks simply add an inclusive condition to the Imperial dialogue such as OR GetIsRace YourCustomRace == 1 the issue with doing that is it can cause conflicts with other mods that alter that dialogue quest. Another option is to make new dialogue for your race, but that can be time consuming if you want them to have voices. :foodndrink:

If you want to make your race playable, this tutorial will help: http://cs.elderscrolls.com/constwiki/index.php/Race_creation_tutorial

So that is the reason I got new races with "DO NOT USE" description from mods... to make them have greetings?

I can't say with 100% certainty, but that is one possibility.

OH that would explain it. It worked fine for quite some time, and then I started a new character and saw these races in the char gen page so I flagged them as unplayable. Hmmm. Well I just made them regular imperials and then modded the imperial race. It started working again after I did that so I'll probably just leave it alone.