Seems to be a group policy setting.
Now don't change any settings unless you are SURE. I have never had this problem so I have not done this myself. Just look to see if you can figure something out.
Click Start> Click Run> Type MMC
In the console window click
File> Add/Remove Snap in
Click Add
Choose Local Computer Policy> Click Add> Click close
Now on the left you'll see a [+] Local User Policy. Click the Plus
then you'll see [+] User Config. Click the Plus
then [+] Administrative Templates
then [+] Network
then Click on Network Connections
Now the right side you'll see lots of things that say
Prohibit access to LAN .. etc etc.. see if any of those are Enabled.
If they are enabled either change them to not configured or disabled.
Becareful to remember what you change. This shouldn't affect Administrator accounts though.. just limited users..
Good luck