Is it true that now for the use of Sniffer on 7.3 - Blizzard begin to block accounts? So you are silent that there is no information about the update on the new build?
*before release 7.3 Blizzard renewed the license agreement. http://eu.blizzard.com/en-gb/company/legal/eula
Maybe your issue is your client if you donwloaded it of a private server site. Did you patch your wow.exe?
Change the realmlist in the config.wtf file (set realmlist "127.1.0.0") of your wow and check in propierties "only read".
Be sure that your wow client version is the same than trinity core version soported.