I wonder if surface calculation is failing more often on Windows.
Your two examples 1jff and 2p4n worked on the Mac (Intel Mac 10.4.11,
Aqua Chimera version 2548) though it gave some warnings. Reply log
output is below.
On Windows, I get an error 5. On Linux, I see ton of SES errors, and it eventually fails over to single-component calculation (error -11) (model 1ffk)