I was recently involved in an issue with file transfers failing between two Lync Online federated tenants. This had worked before, so I was surprised to read it was not supported. The Microsoft Lync Online for Enterprises Service Description (as of October 24, 2011) states:
> File transfer is not available with federated connections
With help from an engineer at Microsoft we figured out the issue was an older Lync client.
One peer had version 4.0.7577.280 of the Lync 2010 client instead of the latest version 4.0.7577.314. After upgrading the Lync 2010 client to the latest release (see Description of the cumulative update package for Lync 2010: July . . . → Read More: File Transfers in Microsoft Lync Online
