Wooohooo! I broke it for you! You're welcome! 
Error information:
Version: 1.0.0.5
<class 'lxml.etree.XMLSyntaxError'>: Opening and ending tag mismatch: folder line 16 and requiredInstallFiles, line 17, column 25
File "fomod\mainframe.py", line 55, in accepted
File "fomod\validator\validate.py", line 29, in validate
File "src\lxml\lxml.etree.pyx", line 3427, in lxml.etree.parse (src\lxml\lxml.etree.c:80041)
File "src\lxml\parser.pxi", line 1782, in lxml.etree._parseDocument (src\lxml\lxml.etree.c:116235)
File "src\lxml\parser.pxi", line 1808, in lxml.etree._parseDocumentFromURL (src\lxml\lxml.etree.c:116585)
File "src\lxml\parser.pxi", line 1712, in lxml.etree._parseDocFromFile (src\lxml\lxml.etree.c:115473)
File "src\lxml\parser.pxi", line 1115, in lxml.etree._BaseParser._parseDocFromFile (src\lxml\lxml.etree.c:110170)
File "src\lxml\parser.pxi", line 573, in lxml.etree._ParserContext._handleParseResultDoc (src\lxml\lxml.etree.c:103644)
File "src\lxml\parser.pxi", line 683, in lxml.etree._handleParseResult (src\lxml\lxml.etree.c:105298)
File "src\lxml\parser.pxi", line 613, in lxml.etree._raiseParseError (src\lxml\lxml.etree.c:104207)
To produce this error is was testing to see if it would recognize missing characters in the code. I changed
<folder source="000 Core" destination=""/>
to
<folder source="000 Core" destination="">
Took out the slash. It broke. :
:
EDIT:
Really it says what it's missing but it's not saying that in a pretty little message box. Just the error. I could use the error to figure out what is wrong, but new users would not be able to determine from that error what is missing.
EDIT2:
Love the "Nobody panic!" title. 
EDIT3:
Same thing if you forget to close a quote ("...") and just leave it ("...).
Error information:
Version: 1.0.0.5
<class 'lxml.etree.XMLSyntaxError'>: Unescaped '<' not allowed in attributes values, line 48, column 8
File "fomod\mainframe.py", line 55, in accepted
File "fomod\validator\validate.py", line 29, in validate
File "src\lxml\lxml.etree.pyx", line 3427, in lxml.etree.parse (src\lxml\lxml.etree.c:80041)
File "src\lxml\parser.pxi", line 1782, in lxml.etree._parseDocument (src\lxml\lxml.etree.c:116235)
File "src\lxml\parser.pxi", line 1808, in lxml.etree._parseDocumentFromURL (src\lxml\lxml.etree.c:116585)
File "src\lxml\parser.pxi", line 1712, in lxml.etree._parseDocFromFile (src\lxml\lxml.etree.c:115473)
File "src\lxml\parser.pxi", line 1115, in lxml.etree._BaseParser._parseDocFromFile (src\lxml\lxml.etree.c:110170)
File "src\lxml\parser.pxi", line 573, in lxml.etree._ParserContext._handleParseResultDoc (src\lxml\lxml.etree.c:103644)
File "src\lxml\parser.pxi", line 683, in lxml.etree._handleParseResult (src\lxml\lxml.etree.c:105298)
File "src\lxml\parser.pxi", line 613, in lxml.etree._raiseParseError (src\lxml\lxml.etree.c:104207)
EDIT4:
And this is from missing an equal sign ( = ):
Error information:
Version: 1.0.0.5
<class 'lxml.etree.XMLSyntaxError'>: Specification mandate value for attribute path, line 47, column 19
File "fomod\mainframe.py", line 55, in accepted
File "fomod\validator\validate.py", line 29, in validate
File "src\lxml\lxml.etree.pyx", line 3427, in lxml.etree.parse (src\lxml\lxml.etree.c:80041)
File "src\lxml\parser.pxi", line 1782, in lxml.etree._parseDocument (src\lxml\lxml.etree.c:116235)
File "src\lxml\parser.pxi", line 1808, in lxml.etree._parseDocumentFromURL (src\lxml\lxml.etree.c:116585)
File "src\lxml\parser.pxi", line 1712, in lxml.etree._parseDocFromFile (src\lxml\lxml.etree.c:115473)
File "src\lxml\parser.pxi", line 1115, in lxml.etree._BaseParser._parseDocFromFile (src\lxml\lxml.etree.c:110170)
File "src\lxml\parser.pxi", line 573, in lxml.etree._ParserContext._handleParseResultDoc (src\lxml\lxml.etree.c:103644)
File "src\lxml\parser.pxi", line 683, in lxml.etree._handleParseResult (src\lxml\lxml.etree.c:105298)
File "src\lxml\parser.pxi", line 613, in lxml.etree._raiseParseError (src\lxml\lxml.etree.c:104207)
Okay...I'll stop now.