Collectible Card Game Headquarters

So I'm trying to install xmage and then i clicked details on why it could not open the app. Could someone please help me or redirect me to a previous post that helped? (There was also a bunch more stuff, but I'm a new user and it told me to remove off-site URLs)

JNLParseException[ Could not parse launch file. Error at line 1.]

Caused by: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.