So the initial load always fails, but the second load always succeeds? If it were related to RAM, it probably wouldn't load at all. Or if VaM couldn't handle that file size, it also wouldn't load at all. Very strange.
I would start by clearing your Cache directory. See if that fixes the behavior. A corrupt Cache file should give you troubles every time though, so I think this is a long shot, but it's an easy test.
Perhaps there is something on the original file that VaM chokes on. How about opening the 16k image into a paintbrush program, saving it to a new filename, and attempting to use that new file? Same issue?
Finally, do you see any messages in the error log inside VaM?
If you wouldn't mind sharing the texture file, I could try it on my setup and see if I experience the same thing.