Hi there,
Do you see any encrypts on the clients? if you do, make sure that you do see those decrypts on the concentrator ( sh cry ip sa ).
If you are seeing decrypts on the pix, then make sure that your pix is also encrypting the traffic ( sh cry ip sa ) and if this is true as well, make sure that your client is decrypting that
Hope that helps to narrow down the problem
Jazib