System error 6 The handle is invalid on Net Use

The user has a 3-user network, all on Win7 Pro, One PC is where they share their files, with a computer name of "Server".  Up until today, the two workstations were mapped to the Server PC using this command:

Net Use F: \\server\c  

This has worked fine for years.  But today they can no longer connect.  If I delete the F: drive mapping, and once again do Net Use F: \\Server\c I get this error:

System error 6 has occurred
The handle is invalid

And if I browse to Network, I can see the PC named Server, but if I double click it I get this error:

Windows cannot access SERVER
Check the spelling....etc....
Details: Error code 0x80070033
The network path was not found

Other details:

1) They use Norton security.  I have tried turning off the firewall and antivirus on a workstation and on the server to no avail.

2) I can still do the normal Net Use mapping on the "Server" computer--but not on the other two PCs.

3) I went to do a system restore on the Server PC, but to my surprise Windows said was disabled--so no help there.

Any ideas?  TIA
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sasllcAuthor Commented:
In the last few minutes two more customers have called in with the same problem--for the first time ever.  I wonder if there was a Tuesday night update to Win7 that is causing this??
Iamthecreator OMIT Admin/EE Solution GuideCommented:

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Net Use F: \\server\c

can you check whether there is still a share named C at Server ?

anyway, you may think of using C$ as share name or - even better - use a much longer and less easy guessable name with a $-suffix. the $ makes the name invisible in the network for clients with their windows explorer.


iamthecreator is right. i also got a message that the update KB4480970 deactivates the Network Controller on Windows 7 and Server 2008 systems such that shares at a server are no longer accessible.

You have to uninstall the package for example by the command

   wusa.exe /uninstall /kb:4480970

at the command line and reboot.

sasllcAuthor Commented:
Out of all the customers that have called us this morning, so far that registry edit has worked:

reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\system /v LocalAccountTokenFilterPolicy /t REG_DWORD /d 1 /f
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