I\'m ask/answering this question because it hung me up & it\'s likely someone else will have the same problem.
Install of RabbitMQ x64 v2.8.6 on Windows Server 2
This problem still occurs in Erlang 18.3 (erl7.3) and RabbitMQ 3.6.9 on Windows when upgrading from any older version of RabbitMQ to version 3.6.9. The solution as already stated here is to manually set ERLANG_HOME with 'setx -m ERLANG_HOME "C:\Program Files\erl7.3"' before starting the service.
What happens is that the RabbitMQ 3.6.9 installer removes the environment variable ERLANG_HOME from the system while removing the older version of RabbitMQ. Then, when it proceeds to the installation step, it does not put back the ERLANG_HOME variable. Then, the batch files that start up RabbitMQ cannot find Erlang. They try to find Erlang's home directory using "where.exe" but it always fails after an upgrade.
RabbitMQ's installer also does not kill all of the Erlang background processes, causing many of its files to be undeletable due to the Windows "file in use" problem. This leaves behind "files in use" in %APPDATA%\RabbitMQ and "C:\Program Files\RabbitMQ." These processes are "erl.exe," "erlsrv.exe," and "epmd.exe." The RabbitMQ installer should taskkill these processes after shutting down the RabbitMQ Windows service.
RabbitMQ is rather clunky on Windows.