I’ve been getting these errors:

W: There are no public key available for the following key IDs:
A70DAF536070D3A1
W: There are no public key available for the following key IDs:
A70DAF536070D3A1
W: You may want to run apt-get update to correct these problems

and found a fix (I think) here:

http://www.debian-administration.org/users/dkg/weblog/11</a>