Never had this happen before. I have a clean install of 3.1 and a MK2cr. I am instaling the drivers from aminet as I have done before. It will not open and the screen flashes and it says that the drawer can't be opened?
-A
I had the same thing happen to me so I did a google search and it brought me here

As the others said the ICON was there but the actual folder(drawer) was not.
I could not create one as I got the error "already exists" but i just deleted the icon file (.nfo) and recreated a new drawer and BOOM it worked.
I then copied whatever monitors i wanted in there rebooted and it was fine.
I checked the WBdisk floppy i installed from and this had the same problem so i suspect you and i have the same bad copy image for the wbench31.adf file.
I have since re-imaged a copy from my original. I am sure you probably figured it out by now since your post but I thought I'd share in case someone else had the issue as I also did.