According to cpn.canon-Europe, DPP 4.0 is only compatible with 64-bit OS...so why would I have to have the 32bit version of photoshop installed??
I'm only pointing out what the user guide says, not explaining it. Its likely that not all the components of the program are 64 bit. I've copied the section and highlighted the pertinent info in Red.
From the Help Section:
Transferring a RAW Image to Photoshop
A RAW image can be converted to a TIFF image (16bit) and transferred to Photoshop.
Select the [Tools] menu → [Transfer to Photoshop].
Photoshop starts up and the transferred image is displayed.
A single image can be transferred at a time
Only one image can be transferred at a time. To send multiple images at a time, see "Batch Transfer Images to Image Editing Software".
Compatible versions of Photoshop are 7.0 or later.
Transferred images are automatically converted to TIFF images (16bit) to which an ICC profile is added. The ICC profile contains information about [Preferences] (Color Management) or work color space set for each image as described below and the appropriate color information is relayed to Photoshop.
When you exit Photoshop, only the original RAW image remains, and the transferred image will disappear. Saving the transferred image as a separate image in Photoshop is highly recommended.For CS4 or later versions of Photoshop, this function is not available if a 32-bit version is not installed.