This error means that there is a mismatch between the Logon Rights permitted for that user and the LogonType that is requested by dbFront.
dbFront allows you to specify how it should process the Logon requests. To see where that is set please see: Application Service Setup
By default the LogonType of 2 (Interactive) is used. This means that the user must have the privilege to complete an interactive logon (e.g. at the console or RDP)
Depending upon the scenario this might be considered dangerous since you don't want users to be able to logon to the server.
For that reason many networks give those users Network access. That would equate to the LogonType of 3 (Network).
For more details on the different LogonType's see: http://techgenix.com/Logon-Types/
To manage a users Logon Rights you can use an old Windows 2003 Resource kit utility named NTRights. This utility still works on current versions of Windows. More details can be found at: