Sorry for my late response, I got my master degree this week.
So, basically flash supports the concept of MorphShapes, which are vector drawings that includes information about how they change over time. Lightspark currently partially parses the data structure for MorphShape, but does not attempt to render them.
The error you get comes from the parsing code for such morph shape, you can take a look at src/parsing/tags.cpp and src/swftypes.cpp as those files contains most code related to parsing, in particular the following classes:
std::istream& lightspark::operator>>(std::istream& s, MORPHFILLSTYLE& v)
is the one where the error happens, it should be fixed to support the other fill styles, you can take a look at the parsing of FILLSTYLE and the official swf10 spec to understand the meaning of the fields.
Please drop by in #lightspark IRC channel on Freenode if you have other questions