Please download and try this updated Cache Relocator zip file. It should default to "This PC" rather than "Desktop" when browsing for folders, and display all available drives.
Another reason for this problem may be due to a Windows peculiarity: if there are too many files/folders/icons on the Desktop, the "Browse for Folder" Windows dialog can't handle it all. It displays the user's personal folders in the list, but the disks and the Computer/My Computer/This PC items may be missing. In such case, you simply need to clean-up your desktop and remove the items you don't use anymore.