The Error itself is normally self explanatory. In that you could have simply entered in the wrong username or password.
If you are sure, however, that the username and password is correct; then by clicking on Error Details, this will provide you with a more detailed error as to why the ADM Client application is returning the Login Error.
Within the Error Details text, look for further information as to the cause, within the Inner Exception trace of the Error.
Some samples of the Inner Exception errors and their meanings:
Unable to log in to ADM Invalid User Details!
The chances are that you have not supplied the correct Login details.
If you are unable to log in to ADM due to Invalid User Details speak with your ADM Administrator. They may be able to reset or advise your password.
Unable to log in to ADM The ADM application needs to be upgraded!
It is very likely that the Application is not the same version as the Database.
If you require a different version of the ADM Application
The transaction log for database '<ADMdatabasename>' is full due to 'LOG_BACKUP'
Could indicate that the ADM Database Log file's have grown quite large and there is not enough space on the System Drive of the SQL Server to execute queries on the Database.
If you are seeing the Inner Exception error The transaction log for database '<ADMdatabasename>' is full due to 'LOG_BACKUP' you will need a to speak with your IT about this as this is an environmental issue and will need resolving internally.