one or several characters couldn't be converted correctly from cp936 to utf-

It seems like you are encountering an encoding issue. This error message indicates that some characters in the cp936 encoding (which is commonly used in Simplified Chinese) could not be converted to UTF-8 encoding properly.

To resolve this issue, you can try to decode the cp936 encoded strings into Unicode using the correct encoding method and then encode them into UTF-8. Alternatively, you can try to set the encoding to cp936 when reading the file or processing the text.

For example, in Python, you can use the `decode()` method to convert the cp936 encoded string to Unicode and then use the `encode()` method to convert it to UTF-8. Here's an example:

s = '你好世界'
s_cp936 = s.encode('cp936')
s_unicode = s_cp936.decode('cp936')
s_utf8 = s_unicode.encode('utf-8')

I hope this helps! Let me know if you have any other questions.