Attached Link: http://www.castironflamingo.com/tutorial/grouper/index.html

Ahhh...ok...the invalid format error is usually something bad in the polygons created by the posing you did. The simple fix is a freeware program called Grouper. The link is the download page and has some explanation of how to use it. This problem killed me for awhile...grouper has fixed every one of the errors I've gotten.