I created a custom weather file with the weather file converter provided by energyplus for illuminance simulation. The changes made are Globla / Direct Normal / Diffue radiation values. I converted the .epw file to .csv to open it in Excel, modified the .csv file, and changed it to .epw file again. I attached the screen when an error occurred.
When I opened the .csv file, there were a few broken letters. It is assumed that the file was opened in a computer environment using Korean. Because the file with the broken character can not be converted back to the .epw file, it was deleted from the .csv file before conversion to the .epw file. I'll add if this could be the reason.