Installation of the first Exchange server in the organization can't be delegated [DelegatedMailboxFirstInstall]
Exchange Setup can't continue because this is the first Exchange server in the organization, and the first Exchange server needs to be installed by a member of the Enterprise Admins security group (to create the Exchange Organization container and configure objects in it).
Note: If you haven't already extended the Active Directory schema for Exchange, you need to do one of the following steps:
A member of the Schema Admins group can extend the Active Directory schema using another computer in the domain before you install Exchange.
Exchange Setup can extend the schema if your account is a member of the Schema Admins group.
To resolve this issue, run Exchange setup again using an account that's a member of the Enterprise Admins security group (add the current account or use a different account).
Having problems? Ask for help in the Exchange forums. Visit the forums at: Exchange Server.