I've had this problem for a couple weeks now. I've created a simple model in maya, rigged it the proper way and exported it as a dae file. Normally I don't have a problem uploading it as a rigged item in SL. Now however, the skin weights option is grayed out in the upload box. I've tried different models, different skeleton, different viewers and different computers. I've used Maya 2011 and 2012 and both with the same result. I've looked and looked and haven't been able to find an answer so if anyone has an answer to this, I would really appreciate it!