Adding network share as the system account breaks Win7 backup to network

(On Win7 Ultimate x64 SP1)
So I've been using Win7 backup to \\192.168.0.100\Backup\main-desktop\ for a while without issue.

Yesterday I tried to setup crashplan to synchronize my dropbox folder and a network share. I then found out that crashplan, as it runs under the system account, can't see my user mapped drives. So I created a startup script

net use O: \\192.168.0.100\Documents /USER:192.168.0.100\username password

and set it to run, on startup, after the network interface is up, as the system account. (the username & password are the same for the net use script above, the locally logged in user, and the explicit username/password entered in windows backup).

I woke up this morning to find error flags from the windows backup and get "Network location cannot be used" (0x800704B3).

If I disable the startup task & reboot then windows backup works fine.

I'm not sure why having a mapped drive for another user is killing windows backup (same server, different folder). I can work around the issue by using another program to synchronize the two folders, but I'm completely in the dark as to why this happens (and it's 100% repeatable). Uninstalling the crashplan client doesn't change anything - it's the net use run under the system account that breaks win7 backup (to a network location).

Got a partial answer (full functionality work-around, still no idea as to the cause of the instability) from this link: Ars Technica Forum Post

I'd suggest looking into this TechNet article. I came across it while trying to figure out why some of our domain logon scripts that worked under XP wouldn't work under Win7. I never actually implemented the suggested fix, because it turned out to be a better idea to get rid of the old, utterly pointless logon scripts, but it sounds like your situation may be similar enough that it could help you.

Basically I applied the referenced registry fix, changed the crashplan service to run under my user account "with highest permissions", rebooted, and it was then able to see the network drives without causing instability.

The actual registry key suggested by the referenced TechNet article is:

1.Click Start, type regedit in the Start programs and files box, and then press ENTER.
2.Locate and then right-click the registry subkey HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System.
3.Point to New, and then click DWORD Value.
4.Type EnableLinkedConnections, and then press ENTER.
5.Right-click EnableLinkedConnections, and then click Modify.
6.In the Value data box, type 1, and then click OK.
7.Exit Registry Editor, and then restart the computer.