Question

Does anyone know if there is a way to make an Excel 2003 Document Level Customization work with Excel 2010? When I try to execute this document level customization built on Excel 2003 and VSTO 2005 SE, I get the following error.

“The assembly * could not be found at or could not be loaded.

You can still edit and save the document. Contact your administrator or the author of this document for further assistance.”

Any help would be appriciated.

Answer 1

Just to share with people what I’ve learned thus far.

Office 2010, specifically in this case Excel 2010, has 64bit compatibility issues with Document Level customizations and I think Add-Ins when executing solutions built on Excel 2003 files. This appears to be an issue more specifically with Visual Studio Tools For Office SE (VSTO) where the OTKLoader.dll, being 32 bit, can’t be loaded by Excel 2010 64bit version.

Our specific test was to take an Excel 2003 Document Level customization built by Visual Studio 2008, and install it on a Windows 7 64 bit machine running Office 2010 64 bit. The error received is the error as stated in my original question.

We then took a Windows 7 64 bit machine running Office 2010 32 bit and installed the Office Business Application. The OBA, the documen level customization, executed without error.

You’ll probably want to reference the following article from Microsoft.

“Compatibility Between the 32-bit and 64-bit Versions of Office 2010”
http://msdn.microsoft.com/en-us/library/ee691831.aspx

I personally haven’t made it through the article completely, but there’s enough descriptive text and some explict statements that lead me to believe that Office 2003 customizations, currently, are not compatible with Office 2010’s 64 bit version.

Hope that helps someone out there. This was a real pain to sort out.

Note the options we’re presenting at this time are to:
A: Only allow 32 bit versions of Office 2010.
B: All Office / Excel 2003 Document Level Customizations must be upgraded, at a minimum, to Excel 2007 solutions.