You send a large file by using Microsoft Office Communicator 2007 R2 and a Microsoft Office Communications Server (OCS) server that has the Microsoft Forefront Security for Office Communications Server (FSOCS) component installed. In this situation, you may receive the following error message after one minute:
"Cannot send <filename> to <username>".However, if you keep the file transfer instant messaging (IM) session open, the recipient can eventually receive the large file from you.
When a FSOCS component is installed on an OCS server, file transfers are routed to the OCS server for a virus scan. When the file transfer starts, the Office Communicator client sends a Session Initiation Protocol (SIP) messages to the OCS server, but it ignores the provisional responses that are received from FSOCS. Therefore, a timeout occurs after about 60 seconds and then you receive an error message. However, it does not stop the actual file transfer. The file can still be sent to the recipient successfully.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.