.net - Excel VBA error when calling DLL "An attempt was made to load a program with an incorrect format"

I have an Excel file that calls a .net DLL (called "MyDLL") in the auto_open VBA macro.
When it gets to the 2nd line below, the error below occurs:

--VBA Code--

If objSensitivity Is Nothing Then

Set objSensitivity = CreateObject("MyDLL.Calculations") '<

--Error--

An Error has occured: -2147024885

Automation error
An attempt was made to load a program with an incorrect format.

My system is:

• A Windows 7 64-bit PC.


• It has Excel 2003, 2007 and 2010 installed (x86)


• It has .Net Framework 1.1, 2.0, 3.0, 3.5 and 4.0 installed for both x86 and x64


• It has all the latest windows updates.

Other notes:

• I know that the DLL was created in VS2005 in VB with a Target CPU setting of 'AnyCPU'


• It makes no difference if i change the Target CPU setting of 'X86' - the error still occurs.


• I recently had to rebuild my PC due to a hard drive failure, and before that it worked fine. So i dont know what has happened for it to not work now.


• The issue occurs in all versons of Excel i open the file in.

Since i know that it worked fine previous to my rebuild, and i know it works for other users running it on Windows 7 64 bit, i can only assume it is something else specific to my PC, and not the actual DLL.

Can anyone help?

Answer

I sorted this out.

I did a repair install of all my versions of Office, as i suspected it was a faulty Microsoft Interop DLL OR for some unknown reason, it was using a 64-bit version of the Interop.

Very weird, but its up an running now.