I was having the same problem yesterday. I think the server was clogged. Can you try downloading OneCare today? If you receive the same error message. Can you start BITS manually?
To start Background Intelligent Transfer Service (BITS) manually:
1. Click on Start>Run
2. Type in Services.msc then click OK
3. look for Background Intelligent Transfer Service (BITS) and start the service.
4. Download OneCare v2.0 beta if you receive no error in starting BITS.