If you edited a .cht file on a Mac or a modern Windows text editor, it might have saved as UTF-8. GenPlusDroid, being an older codebase, may reject this. Open the .cht file in a proper text editor and with ANSI or ASCII encoding.
Use websites like:
Typically formatted as an 8-character alphanumeric string with a dash (e.g., RFGA-A6X4 ). These codes directly patch the ROM data. genplusdroid cheat file portable