Code stopped working. URLLoader

This time last week I had a simple working app that I was running from inside Flash CS3 Pro because the output I wanted was in text format and I was using trace() to get it to the output console.

2 days ago I ran the code again and got an “Error opening URL” message. The URL still exists and is reachable from the machine the code is running on. As far as I can tell nothing has changed but suddenly the code has stopped working.

I’m using URLLoader.load(URLRequest) to do the work.

Have I changed some security setting by mistake or has an update done this in the last week or so?

Any hints as to where to look would be helpful.