Cannot add DLL reference with AddFromFile - excel

Question

I am trying to use a COM visible .NET DLL from Excel VBA. I have been successful when registering the DLL using regasm and then manually adding a reference to it via the Tools -> References menu item in the VBA Developer window.
However, I am now trying to register the DLL without using the regasm command so that the Excel file can be used on any computer without registering the DLL. So far this is what I've tried:
Dim JART_Instance As Object
Sub Initialize()
Dim RefPath As String, X As Byte
Const RefName = "JART xxx"
RefPath = Application.ActiveWorkbook.Path & "\JART\JART.dll"
With ActiveWorkbook.VBProject.References
For X = 1 To .Count
If .Item(X).Description Like RefName Then
.Remove .Item(X)
End If
Next
.AddFromFile (RefPath)
End With
End Sub
Sub PostInitialize()
Set JART_Instance = New JART.MainJobControl
End Sub
I have added a reference to "Microsoft Visual Basic for Applications Extensibility 5.3". When I run the above code I get "Run-time error '48': Error in loading DLL". I have loaded this DLL a couple times using regasm. Do I need to do something like change the GUID's used in the project and retry. I've seen code examples where this is supposed to work.
If I reference the tlb file instead of the .dll I do not get the DLL loading error. Instead I get an error whenever I try to use the JART_Instance variable saying that the reference has not been set. Even though PostInitialize gets called directly after Initialize and there is no evidence that any of the code threw an error or failed to run. If I try to put a "Stop" command in the PostInitialize function it tells me that it "Cannot enter break-mode at this time".
Any ideas, thanks.

Answer 1

Excel-DNA has a helper function that does this for Com Addins written on that platform.
It appears to:
load the addin
register it with CoRegisterClassObject
add it's progid to the registry
add it to the registry key HKCU\Software\Microsoft\Office\Excel\Addins
call Application.ComAddins.Update in Excel
remove all the previous registry entries
Unregister the object with CoRevokeClassObject
It would appear that once Excel has loaded the addon, it doesn't unload when the registry entries are removed and CoRevokeClassObject is called. It stays loaded until Excel closes and releases it.
So, it's doable but not easy.

Answer 2

Okay so I've resorted to doing a shell command to register the DLL with regasm. Here is my code:
Private Sub Workbook_BeforeClose(Cancel As Boolean)
Dim strWinCmd As String
Dim retVal As Double
strWinCmd = "cmd.exe %SystemRoot%\Microsoft.NET\Framework\v2.0.50727\regasm.exe /u /codebase /tlb .\JART\JART.dll"
retVal = Shell(strWinCmd, vbHide)
End Sub
Private Sub Workbook_Open()
Dim strWinCmd As String
Dim retVal As Double
strWinCmd = "cmd.exe /c %SystemRoot%\Microsoft.NET\Framework\v2.0.50727\regasm.exe /codebase /tlb """ & Application.ActiveWorkbook.Path & "\JART\JART.dll"""
Call Shell(strWinCmd, vbNormalFocus)
Call Button_Handlers.Sleep(1500)
Call Button_Handlers.Initialize
End Sub
For reference the Button_Handlers.Sleep just calls the system sleep method and Button_Handlers.Initialize does this:
Sub Initialize()
'This JART.MainJobControl is the main class in the JART DLL
Set JART_Instance = New JART.MainJobControl
'Use JART_Instance
End Sub
So basically I'm trying to register the DLL at start-up and un-register it on close. My problem is that when I open this file on a new PC I get an error in Button_Handlers.Initialize. It tells me that I'm trying to use an undefined class (JART.MainJobControl), as if the DLL wasn't referenced. If I try to reopen the file everything works fine???
The way I'm doing this is manually adding the reference to the DLL on a machine that already has it registered with regasm. I then save this excel file and transport it to a machine that hasn't had the DLL registered and try to open it and run it. I think that since the reference is already added to the excel file, alls the code has to do is register it with regasm. Does anyone know why this wouldn't work? Am I not sleeping long enough. I may post this as a separate question.