Can you post the tileset you're inserting? If any tiles have colours that aren't in the tileset's palette they'll just become the background colour, which is yellow. So maybe that's the case with the left part of your tileset.
Just tried with a clean ROM and have the same problem. I'm using AM 1.92. This is the full tileset:Have you tried a different ROM? And can you post the tileset you're trying to insert anyway?
Okay, this is confusing. The same error occurs in AM 1.95 but it also says that the dimensions for the tileset are wrong (and gives different required dimensions for tileset 0 and tileset 6) which made me wonder if that was causing the problem. I'd used 128x256 as specified in this tutorial. Is there something I don't know about tileset sizes? Thanks!