A very small number of user may experience issues with being able to select their User folder. This is likely due to the home folder being located on a network drive. Due to Apple's sandboxing rules, Disk Doctor cannot open home/user folders on network drives as OS X does not grant the application permissions to view files on networked drives.
If you are not using a networked drive, then please submit a support ticket and we will be happy to further investigate the issue you are experiencing.
Please note: After you press the 'Select User Folder' button, a popup dialog will appear. On this dialog, just press the 'Choose' button in the bottom right corner. Do not try to navigate or select any folder, just press the 'Choose' button.
For more information regarding your home/user folder, please read the following Apple support article: http://support.apple.com/kb/PH10939