It would probably be better if Vault.exe assumed localhost if not specified, since not all commands accept a -host flag. We'll add to our list to pass -host localhost (for commands that require it) if not specified in the action itself.
For now, you can add a temporary Run Script action (VBScript) to your project and rebuild it to change all Vault steps with a blank Host field to 'localhost':
Code:
' change all blank Host fields on Vault steps to localhost
For i = 0 To vbldStepCount-1
For Each objStep In Application.Project.Steps(i)
If objStep.Action = "Vault" Then
If Len(objStep.Property("Host")) = 0 Then
objStep.Property("Host") = "localhost"
End If
End If
Next
Next
Alternatively, you could update the Host property to a macro reference (i.e., "%VAULT_SVR%") and create a project macro with that name and a value of localhost (to make it easier to point your project to another server if needed in the future).