Hsaddin.dll Is Not A Valid Add-in

[Mickie Bottiglieri]

Iam working on an Outlook Add-in which works perfectly when loaded from the registry but it seems impossible to load it manually. When trying from the Outlook File > Options > Add-Ins > "Manage -> Go..." and manually select the dll or Vsto file, I receive the message "MyAddIn is not a valid Office Add-In".I tried with admin right on the machine.Any idea why?

If you want to add and load your add-in manually make sure the assembly you point implements the IDTExtensibility2 interface. Otherwise, you will end up with an error message. In the case of VSTO add-ins, you may try to point to the .vsto file.

Since you mentioned C++ I assume that you are referring to an unmanaged COM add-in. In addition to the usual registry entries for a COM object, the progid of your add-in should be present in the 64-bit view of the registry under HKLM or HKCU Software\Microsoft\Office\Excel\Addins\ with an entry specifying "LoadBehavior" that is usually set to a REG_DWORD value of 3.

I don't have an Excel\Addins key in either HKLM or HKCU. But I don't have any Add-Ins registered with this Excel. The dll I am trying to add is reported as "not valid" so I have stopped at that point. If I proceed, it tries to open the dll as a worksheet.

I didn't write this add-in and the author is no longer available. All I know is that it works with 32-bit Excel. If you could direct me to some instructions for preparing C++ Excel Add-Ins, that would be helpful. The websites I have tried to use are just broken links.

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