Debugging Flex applications with mm.cfg and flashlog.txt let us track trace statements and error messages for projects running in the browser using the debug mode. Since I haven’t done it since 2001 I completely forget what to do and came across couple of issues, so I figured I’ll throw a post for other people that may have the same issue.

You first need to create the txt file and directories here:
/Users/YourUserName/Library/Preferences/Macromedia/Flash\ Player/Logs/flashlog.txt

Then you need to create the mm.cfg file in both location:
/Library/Application Support/Macromedia/mm.cfg
/Users/YourUserName/mm.cfg

Then paste the follwing code in the mm.cfg:
ErrorReportingEnable=1
TraceOutputFileEnable=1
MaxWarnings=0

Initially, I pasted the code only in the first directory and couldn’t get it to work, not sure why, so place the file in both directories to play it safe.
I am running the Flash Debug Player 10, on Mac OS X.

To see the messages as they come on Terminal, navigate to the flashlog directory and type in:
tail -f flashlog.txt

I Hope you find this tip handy.