Here is few steps
1. For standalone application, ensured you have installed debugger version of flash player & always give path of .SWF file to profile, close all browser instances. You can check for flash player version by right click on Flash player & Click on last option which will like "About Flash Player 10....."
2. For web applications, ensure you have made change in WEB-INF\flex\flex-config.xml before deployment as
3. Change perspective to Flex Profiler & ensured you close all of your browser instances.
4. Goto Profile Menu --> Profile an external application, & give path as http://localhost:8080/myProject/myProject.swf
for more information: