Can 32-bit Excel Add-Ins work in 64-bit Excel at all?

Question

Recently since I moved to Excel 2010 64-bit I discovered that many add-ins (XLLs) I used regularly stopped working (Excel reports an "invalid add-in" error when I try to add it).

Does it always hold that 32-bit built add-ins are never compatible to 64-bit Excel, or is it just the case of my add-ins?

Answer 1

32-bit plug-ins won't run in IE 64-bit. 32-bit drivers won't run under 64-bit Windows. 32-bit add-ins won't run in 64-bit Office. It's not just you, it's because 64-bit programs can't load 32-bit modules.

Please see Compatibility Between the 32-bit and 64-bit Versions of Office 2010

"Native 64-bit processes in Office 2010 cannot load 32-bit binaries. This is expected to be a common issue when you have existing Microsoft ActiveX controls and existing add-ins,"

One more link from MS about the differences between 32 and 64 bit versions of Office, and how 64-bit versions cannot run 32-bit add-ons.