Make sure the computer is turned on and is connected to the network. You may also get this error if necessary windows services have been disabled.
This is also why when you do \\computername scheduled tasks is not showing.
The following services need to be running for the push to work:
Step 1. To verify that the following services are running please click Start, Run(Search for Vista and 7 users) type services.msc and then click OK.
Step 2 . Double click on the above services and make sure that they are all running. If they are not start them and make sure they are set to automatic.
These are set to automatic by default when the computer is joined to the domain unless somebody went and changed them later.
Step 3 . If you cannot access the client via \\computername and have the Windows firewall enabled follow the steps here.