As of OnBase 18, when using the graphical installer to install the Mobile Applications Broker Server, it is installed as a 64-bit application by default. In versions prior to OnBase 18, the Mobile Applications Broker Server could only run as a 32-bit application.
If you are manually installing or upgrading the Mobile Applications Broker Server from a version prior to OnBase 18 and want it to run as a 64-bit application, the application pool for the Mobile Applications Broker Server must have the Enable 32-Bit Applications option set to false.