App Not Starting in Debug Mode

I have not worked on a web application for a few months…

But today I created a new web and just hit run without changing anything . It starts the browser with a web page titled “Launching…” and that is as far as it gets. Eventually a fatal error message appears in the browser - This application has encountered an error and cannot continue. And that is it.

I have cleared all the caches, switched default browser etc and no dice. I went back to an old project and the same issue… if I compile either project as an exe, I can browse to it in the browser, without issue. But not in debug mode.

Any suggestions…

I’m on a Mac using 2019.3

I would check that the debug port isn’t being used by another app and that it is greater than 1024.


Hi Wayne,

Thanks for the tip, it at least unblocks me. But it does not really fix the problem.

By giving it a new debug port number, I can get the debugger to work, so that is good and I can see the the debugger is listening on the port (using lsof). But when I exit and come back in, it’s the same story! I need to give it yet a different port number to get it going again and I can’t see anything listening on the old port number.

There is something weird going on but I just can’t put my finger on it…

Check to make sure that the old app is actually quitting.

The other thing to know is that macOS doesn’t free ports immediately. It takes somewhere between 5 and 15 seconds for the port to be available for use again on my machine.

Thanks guys, that seems to have got me over the hump!