The pre- and post- commands are executed on the media server, not on the remote server. If you want to execute a program on a remote server, then you need to put in the full path of the program, e.g.
\\ServerA\c:\Program files\Directory A\program_A.exe where ServerA is the remote server. Also, the BESA needs have have the necessary permission to read and execute the program on the remote server. Whatever commands or programs included in a batch file would also have to be properly qualified.
Before using the batch file as a pre-command, you should test it by executing it from the media server.