EVault 10 / OWA Exchange 2010 / no access to Vault

Hello,

i have trobule with OWA on an installation. Enterprise Vault 10.4 / Exchange 2010 CAS / DAG.
Install an Config Guide complet. OWA User, Script etc...
 

Customer use Form Based Authenication. After Login in OWA an Open an Archiv Mail, i became an

" no access to this vault" Normaly EV must ask me for Username an Password to open Mail or Archiv Explroer but it doesn't
It looks that OWA take the local User Logindata on the PC an give this to EVault.

Any Idea why OWA do not ask for Passwort ? Normaly with Formed Based Auth i must confirm one time after login to OWA my Username and Password.

Thanks for Help.