If you go to:
(before doing the below, make sure pse 11 is not running)
(this on a windows 7 machine, but should work on windows 8 as well)
C:\Program Files (x86)\Adobe\Photoshop Elements 11
in that folder you should see a folder named Optional Plug-Ins and another named Plug-Ins
Double click on the folder Optional Plug-Ins, right click on the folder that says Import-Export and click on Copy
Go back and double click on the folder that says Plug-Ins, right click in an empty space and press Paste
With any luck you see your scanner on the import menu in pse 11
Thank you very much R Kelly. Your instructions were extremely clear and CANOSCAN LIDE 600F now appears in the PSE11 Import box! Now I can get back to work.
I might add that when I went back into Plug-ins and opened the Imports-Exports folder to see if TWAIN was there, it appeared as Twain_32 which I will assume is correct despite my operating system, Windows 8, being 64-bit.
Thank you again. Grateful for your help.