pitching in with a suggestion. if you use ps, illustrator or any kind of batch editing tools, might make sure the file extension is also lower-case. You can use
this tool to rename, search & replace, change case, so on and so forth
in bulk.
And make sure to test both in debugging and release modes. I used to do:
LoadBitmap(File.DirAssets, "\folder\file")
Worked in debugging, file no found in release.
Seems eliminating the slash before the folder name fixes this.
Best of luck!