Scott,
We are in the process of deploying Alfresco but the symtoms you describe are similar to those we are experiencing with an unrelated application using Novell Netware file servers. We've found that when the request, e.g. writing a file to a share, from an automated process within a client and the file is very large, the buffer on the file server which is hosting the share, fills it's buffer to handle the load then runs out of buffer, causing the automated write to fail with no errors present on either the client or server operating systems. The client process, i.e. the application that is executing the automated process, might log an error.
I haven't encountered this problem when performing this function within an interactive session. Also, we haven't, to do, seen this behaviour when the server hosting the share is a 64bit operating system.
Having said that, the Novell Netware is 32bit and using CIFS (TCP 139) but our 64bit clients are running either Linux or Windows Server (majority) and using SMB (TCP 445). Is your CIFS server running samba or is it a Windows box?
-Cy