If you've done some editing in Photoshop (or Lightroom) and are now having problems re-linking your files and assuming that you were attempting this action through the "Re-linking" in the High-Res Production dialog box,  then in order to correctly "re-link" your updated files, they must be:

1. Located in the same folder as the originally loaded images,
2. Have the same filename as the originally loaded images except the file extension can be .jpg, .tif or .psd. (with version 3.3 or newer, ProSelect also checks for "-edit", "-edit2" etc which Adobe Lightroom creates).
3. Have a "newer" date than the original.
   

In the case of (1) above, you may have moved or copied the original images somewhere else, so you need to make sure the "updated" images are saved in the correct folder for the re-linking to work.

In the case of (3) above, check your camera's date and time. If your camera has the wrong date set (eg a future date) then the original camera file may appear "newer" than your re-touched image file and relinking won't occur.

Hint:
One way to check this is to select the image in ProSelect's main window and do a "Get Selected Image Info" (under the Album menu). The window that opens will show the "Original File Location" and the "Production File location". Normally these are the same unless you have re-linked in production, in which case, the latter one will be pointing to the latest "updated" copy of the image file.