If you removed all references to '%' in the xml file, than you actually got a different, though similar error: '"java.lang.NumberFormatException: For input string: "1,781.00"', which can also be fixed by removing all commas (acting as thousands separators) from the y1value attribute.
However once you get your xml parsing working you'll encounter a different error: 'An error has occurred: $ is not defined'. This is due to the fact that jquery is missing from 18.104.22.168 (we've only recently added jquery to the platform). You can workaround this by placing the following file (000-0-jquery-1.4.4.js ) in the web/scripts folder of the project (next to the files graph.js and jquery.flot.js).
If you do decide to go this way, I urge you to remember to remove this specific file when you upgrade the platform to a version which includes jqeury, as it may interfere with the platform version.
For best results, use the Firefox browser..