>>Usually that comes when you try to load a 32 bit dll from a 64 bit application or vice versa.
>
>This is a 32-bit dll. And, the relation between this and the application did not change. I simply moved that into Windows Server 2008 and it complains. So, I assume either that 32-bit dll can no longer be supported in that environment or it conflicts with a new version in c:\Windows\System32 or else.

Is your website compiled as 32-bit and the application pool set to allow 32 bit applications?