operator-mono-lig: Build fails on Windows

I’ve just purchased the Operator Mono SSm version for this project and when running “build” it fails

Compiling ".\build\OperatorMonoSSmLig-Book.ttx" to ".\build\OperatorMonoSSmLig-Book.otf"...
Parsing 'GlyphOrder' table...
Parsing 'head' table...
Parsing 'hhea' table...
Parsing 'maxp' table...
Parsing 'OS/2' table...
Parsing 'name' table...
Parsing 'cmap' table...
Parsing 'post' table...
Parsing 'CFF ' table...
Parsing 'GPOS' table...
Parsing 'GSUB' table...
Parsing 'hmtx' table...
Parsing 'DSIG' table...
ERROR: Unhandled exception has occurred
Traceback (most recent call last):
  File "c:\python27\lib\site-packages\fontTools\ttx.py", line 399, in main
    process(jobs, options)
  File "c:\python27\lib\site-packages\fontTools\ttx.py", line 373, in process
    action(input, output, options)
  File "c:\python27\lib\site-packages\fontTools\misc\loggingTools.py", line 372, in wrapper
    return func(*args, **kwds)
  File "c:\python27\lib\site-packages\fontTools\ttx.py", line 291, in ttCompile
    ttf.save(output)
  File "c:\python27\lib\site-packages\fontTools\ttLib\ttFont.py", line 172, in save
    writer_reordersTables = self._save(tmp)
  File "c:\python27\lib\site-packages\fontTools\ttLib\ttFont.py", line 211, in _save
    self._writeTable(tag, writer, done, tableCache)
  File "c:\python27\lib\site-packages\fontTools\ttLib\ttFont.py", line 624, in _writeTable
    self._writeTable(masterTable, writer, done, tableCache)
  File "c:\python27\lib\site-packages\fontTools\ttLib\ttFont.py", line 628, in _writeTable
    tabledata = self.getTableData(tag)
  File "c:\python27\lib\site-packages\fontTools\ttLib\ttFont.py", line 646, in getTableData
    return self.tables[tag].compile(self)
  File "c:\python27\lib\site-packages\fontTools\ttLib\tables\C_F_F_.py", line 20, in compile
    self.cff.compile(f, otFont, isCFF2=False)
  File "c:\python27\lib\site-packages\fontTools\cffLib\__init__.py", line 108, in compile
    topDict.recalcFontBBox()
  File "c:\python27\lib\site-packages\fontTools\cffLib\__init__.py", line 2340, in recalcFontBBox
    bounds = charString.calcBounds(self.CharStrings)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 984, in calcBounds
    self.draw(boundsPen)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 979, in draw
    extractor.execute(self)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 301, in execute
    rv = handler(index)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 340, in op_callsubr
    self.execute(subr)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 301, in execute
    rv = handler(index)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 591, in op_rlineto
    self.rLineTo(point)
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 525, in rLineTo
    self.pen.lineTo(self._nextPoint(point))
  File "c:\python27\lib\site-packages\fontTools\misc\psCharStrings.py", line 514, in _nextPoint
    point = x + point[0], y + point[1]
IndexError: list index out of range

Similar errors appear for every single font-file and at the end, it’s all empty (0-bytes) otf-files in the build-folder.

Is there a specific version of the font-tools that it works best with? I’m not familiar with Python and currently at a loss.

Thanks for any help you guys can provide.