Maybe you're not looking for the log files in the right place. The BCM Monitor help file states:
"When the “Log UIP Data” control is checked, BCM Monitor writes UIP messages into log files, which are created in Log folder under the BCM Monitor startup directory. One log file is generated for each monitored system and each module/loop. Log files are named IPAddr_MCDN.log, IPAddr_PRI_BusX.log (where X is the bus number) and IPAddr_BRI_BusXModuleYLoopZ.log (where X is the bus number, Y is the module number and Z is the loop number). To view UIP log files, open them with a text editor (e.g., Notepad) or a spreadsheet application (e.g., Microsoft Excel)."
Did you look in the directory that is set as the startup directory for the BCM Monitor application? To control where the log files should go, you can create a shortcut to BCM Monitor and change the "Start in" field in the Properties of the shortcut.