Your XML file isn't well formed.. you can check this using a few different things:
1. Open the .xml file in your web browser. It will give you an error and hopefully give you enough information to determine what's wrong.
2. Open World of Warcraft/Logs/FrameXML.log. This file will also tell you that the file could not be parsed.
In particular you have two things wrong in your opening tag. It should read:
Code:
<Ui xmlns="http://www.blizzard.com/wow/ui"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.blizzard.com/wow/ui/ ..\FrameXML\UI.xsd">
On the second line, you had xmlns:xsl instead of xmlns:xsi (you had an ell instead of an eye). Also, you were missing a closing > after UI.xsd". The file is well formed, other than that.