How to resolve this error: "an unknown item is declared as the root of your mxml document"?

I'm working with eclipse, blazeds and Flex Plugin, and every time I create a Web Dynamic Project then add a Flex Project Nature to it this error: "An unknown item is declared as the root of your mxml document" appears just as the perspective view 开发者_如何学编程changes and I click on the design mode. As far as I know the only lines of code written on the screen are the standard in any other program, but I'll put here anyway so you can have a go at it if there's something realyy wrong and I didn't see:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">

</mx:Application>

Try this...

1. copy the code from IDE to some text editor eg. notepad and try to see if there is any junk character there?

2. If you are using win XP SP 2.0, then update with SP 3.0

Generally the problem occurs when junk characters occur in the lines or the tags are not properly closed.