It took me a while to solve this so I thought I'd post the solution.
On two machines (one 32-bit the other 64-bit) running the new Phonoshop CS5.1 that ships with CS5.5, I had trouble adding a reference in vb (vba) to the Photoshop Object Library for scripting:
I would just get: Error in Loading DLL
It appears that on both machines, the CS5.5 installer incorectly referenced the dll which is called "ScriptingSupport.8li" (not exactly a .dll-looking name but anyway ;-)
The Adobe CS5.5 installer set the system registry to look for the file in:
C:\Program Files\Adobe\Adobe Photoshop CS5.1 (64 Bit)\Plug-ins\Automate
C:\Program Files\Adobe\Adobe Photoshop CS5.1\Plug-ins\Automate
but installed the file to:
C:\Program Files\Adobe\Adobe Photoshop CS5.1 (64 Bit)\Plug-ins\Extensions
C:\Program Files\Adobe\Adobe Photoshop CS5.1\Plug-ins\Extensions
I copied ScriptingSupport.8li from the Extensions folder to the Automate folder and it started working.
Hope this helps someone else. :-)