Can't get correct _LRG image to display

I have uploaded via admin an image top.jpg for a product into the main directory. I have then ftp'd an image top_LRG.jpg into the images/large folder. However, when you click 'larger image' on the live site, the top.jpg image pops up and not the _LRG image.
Where have I gone wrong? Is uploading the top.jpg image into the main directory wrong? Do I have to create a subdirectory (Although what I have read it says you don't)? :unsure:

In the example case you mentioned, the following should work fine:
/images/top.jpg
/images/large/top_LRG.jpg

Remember, the ".jpg" must be the same on both images. You can't have ".jpg" on one and ".JPG" on the other, because technically those are different.

Can you access both images via your browser? ie: http://your_site_name/images/top.jpg and http://your_site_name/images/large/top_LRG.jpg ? If not, then perhaps you haven't properly uploaded the files?

Do you have any addons installed related to images?

:oops:
I had given the main image a .JPG extension. Can't believe I did that. I don't ever use the capitals normally.
Thanks for your help. Changing it to .jpg makes it work fine. Thank you.