I have little to no clue how EMU and stuff works, but what I do know from my personal modding of the official game is that the icons are held in a .GPK file. If the EMU/Client reaches out to a .GPK and the .GPK does not have the icons/dds files for said item it won't show them but give this error.
Likely possibilities if it does reach to the GPK:
1. It searches for it, but can't find it due to a misspelling, wrong name, etc.
Which case you'd have to rename it
2. It searches for it, but can't find it because it doesn't exist.
Not sure if this is plausible or not.