This is how the Dashboard looks like after the authentication

In the stdout_*.log (typically in C:\Program Files (x86)\Enterprise Vault\Dashboard\UI\logs) this error is logged:
An unhandled exception has occurred while executing the request.
System.ComponentModel.Win32Exception (1788): The trust relationship between the primary domain and the trusted domain failed.
The aforementioned might occur in environments with multiple trusts in Active Directory Domains and Trusts
Check in Active Directory Domains and Trusts if there are any orphaned trusts and remove them.
As an alternative it is possible to create a new security group in Active Directory and add the Enterprise Vault System account to it.
Name: IndexingDashboardUser
Group Scope: Domain Local
Group Type: Security

The group named IndexingDashboardUser can also be a local group on each Enterprise Vault Server with the Dashboard installed; therefore add the Enterprise Vault System Account to the same local group