When you are installing Veeam search server according to Veeam Backup & replication 5.0 page 41 it says use a administrator account. When you are preparing for file browsing and advanced searching (page 165) you will add the search server to the Veeam Back-up Enterprise Manager. You can get this error while going trough the wizard.
The problem is that the account doesn’t have enough rights. I went in the configuration of Search server and changed the Standard account for access to the account that is used to run the Veeam search service. ( Sorry picture is in Dutch)
this solved my problem during the add Search server wizard.