Reason:
PowerShell v2.0 or above is not installed in the machine that ADManager Plus is installed, or
Exchange Administrator's credential is not provided in
In ADManager Plus's services if it is installed as a service, or
In the credentials specified for authentication in the Domain Settings.
Solution:
Install PowerShell v2.0 or above in the same machine that ADManager Plus is installed.
Provide the appropriate Exchange Administrator credentials
While starting ADManager Plus services if you have installed it as a service.
In the Domain User Name and Password in the Domain Configuration by clicking on Domain Settings and clicking on the appropriate domain from the list of available domains.