Hi Truong,
Please paste your exception details, it is very hard to guess (maybe
Zed Shaw can do some telepathic assistance, i heard he can do anything
regarding rails 
)
Truong-an Thai wrote:
Hi, production.log and fastcgi.crash.log doesn't show anything.
however, while logging in via ssh shell, I noticed this:
RMagick: Memory allocation failed `Cannot allocate memory'.
Any suggestions?
My best guess would be to add some more RAM to the machine. Or in some other way make more memory available to the process.
The problem with shared hosts is that your memory is limited. As soon as you go over a certain treshold, it just terminates your processes. I’m having similar problems with uploads and even downloads via send_file on a2hosting’s servers. The shell also reads: out of memory, my processes are all killed (including mongrel, the site goes offline) and a core file is dumped. The same application runs without a problem on our VPS or dedicated server.
Best regards
Peter De Berdt