Hi Steve,
It would be good to see the full code and also the stack trace that it generates.
Also, are you working against our SaaS or your own CE/OnPrem instance? if the latter, what version?
Another option you might want to consider for large files, BTW, is the bulk upload method which enables you to upload a CSV or an XML to the server, with the URLs for the files as well as the metadata and then the server will actually download these files and process them or you can use a dropfolder, in which case you simply define a profile where you provide access to this directory via SFTP for example and the server will automatically pull from it and process the files in much the same way.
Thanks,