Dear AccentureDistributionList18000007 ,
Yes, gateway can be used to transfer files. But I strongly recommend not to do so for big files. It's some kind of misusing the gateway. There should be other and better way to do the file transferring, just let gateway do the security jobs like authorization.
Go back to your case, I believe you had set the io.xmlPartMaxBytes to allow big file, then you may check the ssg log (/opt/SecureSpan/Gateway/node/default/var/logs/ssg_0_0.log) to see if any clue of the crash.
I guess you might see Out-of-memory error. If that's the case, in your policy, you might try Configure Message Streaming assertion to enable streaming(ie. no buffering).
Regards,
Mark