100-100 isn't a valid coordinate pair in a polygon (or polyline) 'points' attribute, though it is in a path 'd' attribute. The difference can be seen in the BNF grammars: the 'points' attribute has
coordinate comma-wsp coordinate
but the 'd' attribute has
coordinate comma-wsp? coordinate
The question mark in the 'd' attribute case indicates that the comma-wsp (a non-empty sequence of commas and whitespace characters, containing at most one comma) is optional. But in the 'points' case it is required.
Ideally, scour should give an error message along the lines of "invalid 'points' attribute" or "invalid 'polygon' element", rather than just a traceback.