Slight problem with NT machines network

I have a win 2000 server and 6 NT machines, 4 of them work fine, the other 2 are a slight problem.

When I type \\machine\c$ or \\ip\c$ I don't get access to local C drive whereas with the other 4 that work I do.
I also cannot install sophos on them and get this error message:
Could not access path \\machine\C$\ (Error: 53 - The network path was not found.

However if I type in \\machinename then they show up with printers and schedule tasks and I can ping them quite easily. The network connection between them seems fine.

I need to sort this so I can install sophos and keep the machines upto date as well as allowing me to remotely access the C drive.

Reg key set?

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\LanManServer\Par ameters
Name: AutoShareWks
Data Type: REG_DWORD
Value: 1

You'll need to reboot if you change the setting.

Cheers Geoff, it worked a treat.