I googled and found this:
http://forums.cgsociety.org/showthread.php?t=386320
I was having the same issue. But even trying the workaround I am still getting the error message unexpected failure.
Can anyone confirm?
I select points, go to Envelope/Reassign Locally and select a bone deformer in the Biped Rig (from Biped Guide) and right click. The points don’t get reassigned and I get the error.
I also found this workaround:
https://groups.google.com/forum/?fromgroups=#!topic/xsi_list/3Q51kERFmZ8
Have not tried it yet.
OK got a chance to try that and it seems to fix the error. How in the ***** did he/she figure that out?
Anyways. I guess it is a bug then?