By default the NetAssure box will only allow limited access to iTunes. Specifically if you want to restore a device like an iPhone or an iPad you will need to follow the instructions in this video to allow full access from the client's computer to the iTunes Servers.
Start by looking at this article about which servers and ports to allow:
Once you have done that have a look at this video. It is fairly straight forward to make these changes.
Remember once you have made the changes you should allow up to 30 minutes for the control panel changes to write back to the physical NetAssure box.