I was just trying to transfer some pictures from my PC to my W810i and it works fine. Except I can't find the pictures on my phone (I uploaded them to the same folder as the pictures that are already on the phone). I can see the pictures in MyPhoneExplorer and if I choose to delete them the phone pops up with the question if I want to delete or not.
If you upload pictures into the photos-folder you cannot see it cause the Album-Software from the phone doesnt detect it. Upload the photos into "Pictures" or a subfolder in Pictures and it will work