If the images in the layout files generated by ProSelect's High-Res Production system are incorrect, then ProSelect must be linked to other images. Linked images will always have the same name but with a different extension. eg you loaded image "12345.jpg" into ProSelect but have subsequently re-linked to "12345.tif". 

Any images that are linked to different ones will have the "Link" symbol next to the image name (in Production) and the name of the linked file will appear in the "Selected Item Info" box.  If an incorrect image is linked, then try opening both the original image and the linked one outside of ProSelect and check that they are the same image. BOTH images must be in the same folder.

If you are not sure of the location on the disk for these images, then select one of the images used in the layout (in Working with Images view) and choose "Show Selected Image Info..." from the Album menu. You will find the Original File Location and the Production Image Location listed. These will be the same if not linked and different if linked.

Other things to check:

1. Is this problem happening with all your albums?
2. Try producing Hi-Res images from an album that previously worked. This will help tell whether the problem is with Photoshop or your current Album.
3. Have you changed anything on the computer since it stopped working? eg upgraded Photoshop.
4. Try making a new layout in the same album with the same images and trying building that.
5. If that doesn't work then open a new album, add the images you need for the layout, create the layout and try that.