The activation of dimensions is only allowed when the system is in maintenance mode

In Dynamics 365 Finance and Operation application version 8.1 financial dimensions you have just migrated or created cannot be activated unless the system is in maintenance mode.

At first glance the warning message is quite helpful as it directs you to LCS to put your environment into maintenance mode. However, at time of writing, no such feature could be found in the LCS portal.

Using Microsoft.Dynamics.AX.Deployment.Setup.exe as described in the maintenance mode article (https://docs.microsoft.com/en-us/dynamics365/unified-operations/dev-itpro/sysadmin/maintenance-mode) is not supported on a build environment where you are not admin (i.e. PU12 onwards). This applies until LCS gets this feature. Until then you have to follow the process shown below which is tried and tested by myself on a Tier-1 Build OneBox on PU15 / 8.1

1. RDP onto the Microsoft-hosted dev/build machine
2. Open SQL Server Management studio and connect to the database server using the credentials from LCS for the axdbadmin user -

3. Right click on the AXDB database and create a new query as follows: 

update SQLSYSTEMVARIABLES SET VALUE = 1 where PARM = 'CONFIGURATIONMODE'

4. Restart the “World Wide Web Publishing Service” from the Windows Services app. This restarts IIS.
5. After IIS is restarted, D365-FO will be in maintenance mode

6. Go to your financial dimensions screen and activate your dimensions.

7. When you are satisfied that your financial dimensions are good and active (confirm this by checking if you can add a financial dimension to an account structure in the "Configure account structures" form
8. Get D365-FO out of maintenance mode by executing the following query:

update SQLSYSTEMVARIABLES SET VALUE = 0 where PARM = 'CONFIGURATIONMODE'

9. Restart the “World Wide Web Publishing Service” from the Windows Services app. This restarts IIS.

10. Browse to D365-FO and verify that you are no longer in maintenance mode by trying to activate a financial dimension which should once again show you the warning message shown in the screenshot in the beginning of this screenshot.

Step 10 is very important as if the D365-FO system remains in maintenance mode only users who have the "Maintenance mode user" role can sign in to D365-FO.