Its not actually SGP asking for the location of the catalogs; its actually PlateSolve2 – an independent software application that runs inside of SGP.
This may seem like splitting hairs but it goes to the question about it mattering where the catalogs are located – it doesn’t matter where they are located as long as PS2 knows where they are. The SGP developers have nothing to do here.
Looking in my C:\UCAC3 folder, I see the file “Index.UC3” and 180 files with a naming convention of Z000.UC3 through Z179.UC3. Those would be the files PlateSolve2 is looking for. If you have those files in your folder, its possible something has become corrupted or there may be some kind of permissions issue preventing access to the folder.
Charlie