Make sure the short name and fqdn for each of the following are added to the trusted sites in the Local Intranet Zone on each EV Server in the environment:
EV Server (i.e. ev1 and ev1.yourdomain.com)
Vault alias (i.e. vault1 and vault1.yourdomain.com)
Vault site alias (i.e. vaultsite1 and vaultsite1.yourdomain.com)
so... if you have one EV server in your environment it would be 6 entries per EV server...if you have 2 EV servers... it would be 10 entries per EV server.
Hope this helps,
Rick