My 5th book "50 Tips on JavaScript" is on sale. Go get it from
Illustrated guide to 50 of the most interesting JavaScript topics.

The Flash Builder debugger failed to connect to the running application.

I really don't like FlashBuilder. Mainly because I'm losing a lot of time just to setup the project. Usually when I receive the files I need around 10 hours just to compile successfully. The reasons for those problems are different Flex SDK, different directories' tree, wrong paths, missing libraries or fonts. Today I encounter a brand new type of problem.

This time I got the following error:

The Flash Builder debugger failed to connect to the running application.
Ensure that:
    1. For in-browser applications, you are running the debugger version of Flash Player.
    2. For network debugging on a mobile device, you have a reliable network connection to the device, and port 7935 is open on your machine's firewall.
        Device connection help

I hit F5 key and start waiting. The process bar in the lower right corner looks like that for a long time.

flash builder problem

A new empty page was opened in my default browser - Google Chrome. Nothing happens for a few minutes and I got.

flash builder problem

So, it looks like I'm trying to test the application with a non-debug version of the flash player. Actually Google Chrome has in-build flash player, which is updated automatically. Even if you install the debug one, very soon Chrome will replace it.

Solution #1

Just change the browser. For example, in Firefox the player is installed externally and you are able to install the debug version. Choose Windows -> Preferences and type browser in the search field.

flash builder problem

After that you should be able to see the application.

Solution #2

However, jumping to the browser is not very handy. I mean, while I'm debugging I want to see the console and all my logs there. So, running the application in the browser is not the best option. There is a way to tell that you want to test the compiled swf file, not the html file. They are both inside your bin-debug folder (have in mind that this is the default name of this directory. It could be different inside your project).

Choose Run -> Run Configurations. Pay attention to the URL or path to launch. Uncheck the option, click on the Browse button and navigate to your swf file. It should be in bin-debug folder.

flash builder problem

After that your project will run in a stand-alone flash player.


Use FlashDevelop. It's just better and simple then FlashBuilder.

If you enjoy this post, share it on Twitter, Facebook or LinkedIn. To leave a comment go here.