Not entirely sure what caused this error in the first place, but I’m fairly sure that redoing LDAP settings for my domain controllers fixed it. In SonicWall 18.104.22.1687 you can setup a Filter String that’ll grab users from Active Directory based on whatever criteria you set. I ended up deleting my original LDAP server because it was having trouble saving the UserMap.xml file. Then I setup my PDC and BDC with identical LDAP queries so there would be redundancy.
If you’ve never used LDAP before, you can find a good intro here.
Note: Be very careful that you do not exclude your Admin account or you might not be able to login to administrate anymore. Test the query using the button provided next to the query input boxes and make sure that all your users in ALL of your domains are included in the preview. If they are not then email from them will probably goto Junk and email to them will not be delivered depending on your settings (mine were Rejected outright because of DHA protection).