The sendTimeout affected is in the GUI Core Service client for Web. The following steps will resolve the issue:
1. Open the file /WEB_HOME/web/web.config.
2. Find the following element:
<binding name="StreamUpload_netTcpBinding" maxReceivedMessageSize="2147483647" transferMode="StreamedRequest" receiveTimeout="00:10:00" sendTimeout="00:01:00"/>
3. Modify the sendTimeout that by default is at 1 minute. Raise this to 10 minutes (sendTimeout="00:10:00").
4. Restart the SDL Web Content Manager Service Host and IIS.