I'm not the right person to answer this either but obviously what happens is that your mesh is uploaded as rigid mesh without the rigging. It may be some step you missed in Blander or it may be some export or import setting you overlooked. Have you checked Aine's mesh rigging tutorial? It's a bit outdated but still one of the best, possibly the best, intoductions to Avastar and rigging for SL and there's a good chance the answer is there. The first chapter is here: http://ainetutorials.blogspot.