I've created the following svg file:
<?xml version="1.0" encoding="utf-8"?>
<svg width="640" height="480" xmlns="http://www.w3.org/2000/svg">
<g>
<title>Layer 1</title>
<text xml:space="preserve" text-anchor="middle" font-family="serif" font-size="24" id="svg_1" y="138" x="79" stroke-width="0" stroke="#000000" fill="#000000">Sø</text>
</g>
</svg>
But when I try to open it in Adobe Illustrator I get an error saying it's an invalid SVG file.
This is due to the "ø".
I've been scratching my head, but I can't come up with a solution
You could either use an encoding which supports this character e.g.
<?xml version="1.0" encoding="Windows-1252"?>
or alternatively encode the character. Judging from this you'd replace the problem letter with ø