To check if a drive is on the network  you can use the DriveType
property (3 for network) of the drive object along the following lines.

Sub ShowDriveList()
Dim objDrive As Object
Dim msg As String
For Each objDrive In CreateObject
("Scripting.FileSystemObject").Drives
Select Case objDrive.DriveType
Case 0: msg = msg & vbNewLine & objDrive.DriveLetter & ":
Unknown"
Case 1: msg = msg & vbNewLine & objDrive.DriveLetter & ":
Removable Drive"
Case 2: msg = msg & vbNewLine & objDrive.DriveLetter & ":
Hard Disk Drive"
Case 3: msg = msg & vbNewLine & objDrive.DriveLetter & ":
Net work  Drive"
Case 4: msg = msg & vbNewLine & objDrive.DriveLetter & ":
CD-ROM Drive"
Case 5: msg = msg & vbNewLine & objDrive.DriveLetter & ":
RAM Disk Drive"
End Select
Next
MsgBox msg
End Sub

To restrict usage, you could use the Workbook_Open event to check the
drive type and if not = 3, close the file with "Network Only...."
message.