GetExpandedStringValue: Type Mismatch

This is another post about time painfully spent trying to solve a simple bug.

I'm currently migrating a lot of VBScript code to a VB.NET application. Before you email me about how I should be using C#, please take note that migrating code is already tricky enough as it is so I decided for a language that shares a lot of syntactic similarities with VBScript.

Back to the bug, I was migrating this VBScript code:

      Const C_HKEY_LOCAL_MACHINE = 2147483650
       Dim Server
       Dim strValue
       Dim objReg
       Dim strKeyPath
       Server = "localhost"
       strValue = ""

       Set objReg = GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & Server & "\root\default:StdRegProv")
       strKeyPath = "SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName"

       If objReg.GetExpandedStringValue(C_HKEY_LOCAL_MACHINE, strKeyPath, "ComputerName", strValue) <> 0 Then
           Error ("error reading registry")
       End If

Well, not actually this code but something like this. This works in VBScript but this code in VB.NET that compiles and seems quite the same, generates a "Type mismatch" exception:

       Const C_HKEY_LOCAL_MACHINE = 2147483650
       Dim Server
       Dim strValue
       Dim objReg
       Dim strKeyPath
       Server = "localhost"
       strValue = ""

       objReg = GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & Server & "\root\default:StdRegProv")
       strKeyPath = "SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName"

       If objReg.GetExpandedStringValue(C_HKEY_LOCAL_MACHINE, strKeyPath, "ComputerName", strValue) <> 0 Then
           Error ("error reading registry")
       End If

After wasting a lot of time reading forums and tweaking the GetExpandedStringValue arguments and reading it's documentation, I finally fixed it replacing

Const C_HKEY_LOCAL_MACHINE = 2147483650

with

Const C_HKEY_LOCAL_MACHINE = &H80000002

The final fixed code would be something like this:

       Const C_HKEY_LOCAL_MACHINE = &H80000002
       Dim Server
       Dim strValue
       Dim objReg
       Dim strKeyPath
       Server = "localhost"
       strValue = ""

       objReg = GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & Server & "\root\default:StdRegProv")
       strKeyPath = "SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName"

       If objReg.GetExpandedStringValue(C_HKEY_LOCAL_MACHINE, strKeyPath, "ComputerName", strValue) <> 0 Then
           Error ("error reading registry")
       End If

You might also run into this problem, off-course, with functions like GetStringValue or EnumValues.