Hi Fei,
I did not realize 3DNA v2.0 compiled in 32-bit Ubuntu Linux does work in a 64-bit machine. Yours is the first reported case. Any comment / experience from other users?
Anyway, check email for download link to 3DNA v2.0 compiled in Scientific Linux 6 x86_64. Do report back here if it works, or not.
Xiang-Jun