XML is the underlying language of Quest (different to its coding language) and somehow your game has been modified so it does not conform to XML's rules.
Can you open it in a text edit, such as NotePad? If you can (if not, you are in big trouble!), the top should look like this (the bits in blue will be different):
<!--Saved by Quest 5.6.[color=#0000FF]5621.18142[/color]-->
<asl version="550">
<include ref="English.aslx" />
<include ref="Core.aslx" />
<game name="[color=#0000FF]testy[/color]">
<gameid>[color=#0000FF]ac0b3225-36cd-43ab-b1fc-eb4cdc4af74e[/color]</gameid>
<version>1.0</version>
The first line is a comment. The second line is the start tag for the root element, asl, and it seems to be complaining about that. The very last line should be this:
</asl>
That is the end tag for the root element. Are they both there?
You can also try opening it in internet explorer, which will try to process the XML. It might give more clues if (when) it fails.
Finally you could attach it into a forum post, and we could take a look.