(Taken from the japanese YY-CHR wiki.)
Assuming the loaded file is of a supported image format, this happens when YY-CHR doesnt know where the CHR ROM starts. It needs to be pointed to the correct address. Use the arrow buttons to move around the ROM until the tiles are clear. Visit the Bank View page for more info.
You may have the wrong image format set. Try choosing another, particularly one with less bits per pixel.
If you are expecting certain colors working with a CHR, you need that palette. Either load an appropriate palette file + table combo, or create the palette in the application. For more info, check the palette handling and/or Editor View page.
