Error in make.names(col.names, unique = TRUE) : invalid multibyte string at '<bf><a8><ba><c5>'

This error message indicates that there is an invalid multibyte character in the string. Multibyte characters are characters that require more than one byte to represent them in computer memory.

To resolve this error, you can try the following:

1. Check the encoding of your data file. Make sure it is in a compatible encoding with your system. Common encodings are UTF-8, ISO-8859-1, and Windows-1252.

2. Remove any non-ASCII characters from your column names. Non-ASCII characters are characters that are not part of the ASCII character set, such as accented letters or special characters.

3. Use the `stringi::stri_trans_general()` function to convert your column names to ASCII characters. This function replaces non-ASCII characters with their closest ASCII equivalents.

4. If you are using RStudio, try changing the encoding of your script file to UTF-8. You can do this by going to File > Save with Encoding and selecting UTF-8.

5. If none of the above solutions work, try using a different text editor or IDE to edit your script file. Some text editors may not be compatible with certain encodings.