installed bitcoind 0.10.0 with existing bitcoin.conf from 0.9
rpcallowip format changed
Ah! I thought I was going crazy. Do you recall off hand what the syntax is?
If you were using something like 'rpcallowip=192.168.1.*' before, change it to 'rpcallowip=192.168.1.0/24' (or equivalent that suits your local network).