Not certain about this, but it sounds a lot like the issues that occur with IE on 64 bit (until you've messed around) or on Chrome generally, or on MaxThon (until you've deleted a file from the core installation).
Simply; there is a conflict with the Flash Plugins that you have installed.
You may have installed the debugger plugin, but there is another, non-debugger, plugin that is being chosen by preference. This may be an automatically installed one (as per Chrome), a more appropriate one (64-bit debugger didn't exist at the time I encountered the issue and probably still doesn't, so IE used the 64-bit non-debugger until I uninstalled it), just silly (as per the MaxThon default package that forces their fast mode to use an older plugin due to a frankly quite strange development decision) or just an install conflict (installing a newer plugin that overwrites or blocks the debugger from being used, which is I think what is happening to you).
When you have Flash launched in your browser, right-click and check it is the correct debugger version.
- If it is, then check that your launch path matches the output directory. (I have encountered an issue where a developer was outputting to bin-debug, but testing against bin-release before... Debugger couldn't connect because there was nothing to connect to.)
- If it isn't, which I suspect is more likely, then try uninstalling Flash plugin generally until you get a clean setup and then reinstall the debugger.